Here in the San Jose area I can also get groceries delivered by at least Safeway, Walmart, Google and Instacart (I might be missing some). But personally I'm not using this and I don't know anybody using it.
Online sales make up £6.5 billion of the £170 billion food, grocery and drink sector in the UK [1]. So 3.8%. It's the fastest growing part of the sector.
As these services prefer to deliver larger orders - Ocado's average basket size is £112 according to [2] - the pricing and marketing tends to target families. And obviously, buying and transporting food for 4 people is more bother than for 1 person, so delivery becomes relatively more appealing.
If your friends are mostly young / single, they're not a representative sample of the grocery market.
I lived in London for 5 years and used grocery delivery services a lot. Now I live in Seattle, and don't use them anywhere near as frequently.
There are many difference between grocery shopping in the US and UK cities, but by far the biggest is that in London, a lot of people live without a car. This means walking or taking the bus to the supermarket. (Eg: in San Francisco, 28% of households have no car [1]; in London that number is 60%. [2])
Home delivery allows Londoners to buy the type of and volume of products you want. (I'd rarely buy a 6-pack of 2-liter orange juice cartons alongside the rest of the groceries when I had to walk 30 minutes back from the store.)
Without a car, you also have to make more frequent trips to the store, increasing the overhead of shopping. Being able to drive to the store for a 'big shop' every week or so is much more efficient.
Speaking as another San Jose area reasident, I haven't been to a grocery store in literally a few months -- Instacart is just so much more convenient. Plenty of my colleagues and friends do the same.
These sort of grocery store operated delivery businesses exist pretty much everywhere in the US from what I have seen. They usually aren't advertised, but you can ask about them. I believe they are primarily used by the elderly, handicapped, carless, etc.
When I was in university, a few hundred miles away from my car, I would use the delivery services for very large orders (like 50 liters of seltzer water, or similar). Typically there is a minimum order size, a small service fee, and an expectation that you'll tip the delivery person (who is usually just a grocery store employee who is using their personal car).
I'm from the UK. My colleagues with kids all do their grocery shopping online. They love not having to find time to go to the supermarket, and not having to entertain their kids while they're going round.
From my own experience, it's annoying the first few times you do it but after a while it gets easier. One cool thing is you can have a list of things you regularly buy and easily add them all to your basket. And they know it's harder to get inspiration online so they try very hard to suggest new things to stop you from getting bored.
Publix used to deliver groceries about 10 or so years ago. I used that service from the moment it started to the moment they shut it down. It wasn't viable, because they didn't charge enough, and I would have happily paid more. I miss it to this day, because no one else has started a similar service in my area.
Here in the San Jose area I can also get groceries delivered by at least Safeway, Walmart, Google and Instacart (I might be missing some). But personally I'm not using this and I don't know anybody using it.