Monetizing such a site would be difficult unless you happen to be already the world's biggest bookseller. Thus, any person/organisation with skills and talent to undertake such a task would be better off promoting something with wider margins.
Discounting this reason, and supposing it happened, then amazon could just turn up the dial and throw some resources at it. As things stand, they don't need to.
both of these require very large audiences to make money, the amazon affiliate program pays very poorly and people hate & block ads. Not saying it's impossible but the days of slapping a few ads and affiliate links on your website and expecting to make decent revenue are long gone. Especially if you want to offer a good UX
Actually they aren't long gone at all. Go look at Empire Flippers, Flippa, etc. I build, buy, and operate affiliate and display advertising websites. Lots of sites can make $30 per 1000 visitors just on ads depending on the niche. Some affiliate sites make over $700 per 1000 visitors. Again it depends a lot on the niche.
Also the majority of people do not block ads. This also depends on the niche though. Gaming and tech niches are usually low RPM unless you get targeted affiliate traffic (like you show up on Google for "Best Gaming Laptops of 2021")
would you consider a book reviews website a profitable niche? seems like it'd be a gamble in terms of effort vs reward given that most books are pretty inexpensive
People looking for books online likely have more disposable income than the average population. So I would say ad revenue will probably look pretty good but this is just a guess. Sometimes this can be surprising for different niches. For example, you might not think recipe websites make much money but in fact they often make $30 per 1000 visitors (on ads alone) due to their audience profile. I got turned down offering $140k for a recipe website a few months ago. They were making around $3k per month.
As far as affiliate revenue, they are very likely to be making a purchase soon if they are looking at book reviews so if you can get them to click your Amazon affiliate link there will be fairly high conversion. The revenue per purchase probably is quite low due to the price and margins on a physical book (although I wonder what it looks like for Kindle books) but with enough traffic you can absolutely make it work. I can think of some interesting ways to get a lot of traffic with Pinterest as well in this niche.
This is a numbers game. Keep your costs low and your time involvement low and even if it is only making $2k/month that is good enough because you can have several sites at the same time.
Btw as far as needing a ton of traffic to make money well sometimes that is true to an extent. Recently I was looking at a website that was the most popular user-created website for a specific mobile game. It is generating $6k/month despite having the lowest RPM I've seen so far (only making around $2 per 1000 visitors). Despite this the hosting cost was only $50/mo and I bet I could get that down to $15/month with even better performance.
Side note - you get paid commissions on everything people buy for a certain time after clicking your affiliate link. People buy tons of stuff on Amazon so you'll get lots of revenue for non-book things too.
If you want more info on this type of business model go look at these site (I am not affiliated with them at all):
'...so you'll get lots of revenue for non-book things too.'
If you refer via a the books category and then someone buys from some other random category you get a much lower percentage. This has been a recent move and makes such tactics very unprofitable - for good reason too.
It's not really a "tactic" it's just a side effect of people buying everything on Amazon. You say tactic like it is some slimey technique. You are referring people to Amazon so you get paid for it.
I see a lot of sites grow to thousands in monthly revenue fairly quickly and sell quickly for a minimum of 40x monthly multiple. There are tons of resources and tools out there to build sites that will generate a lot of organic traffic.
It takes a lot of work but if you have the resources practically all of it can be outsourced. What I do is learn as much as I can about each role that is needed, then I hire virtual assistants and train them to do that role. That helps keep costs down since you aren't hiring an "expert".
I'm growing a couple sites right now that I haven't written a single word for or taken a single photograph because I have some awesome writers and a photographer. I've also never posted a single article to Wordpress because, you guessed it, I have an awesome VA that I trained to do that for me. I even have a content manager (the highest paid role) who manages the writers and tells them pretty specifically what to write.
They get paid immediately. It requires capital to run this business. There is always a risk I will lose everything I invested into it. Running this business requires several different roles.
I have been an amazon affiliate for 10 years or more and, to be fair, they behave much better than any other affiliate program I have been involved with.
Lack of an evident business model could be a reason that turns off smart founders from picking this problem. However, if the product adds enough value to enough number of users, one could figure ways to monetise it.
I assume the effort, time and money required to get to "enough value to enough number of users" will require you to answer the "ways to monetise" question for a VC or even yourself before you start.
Discounting this reason, and supposing it happened, then amazon could just turn up the dial and throw some resources at it. As things stand, they don't need to.