Why do asymmetric plans exist in the first place anyway? I assume connections between autonomous systems are symmetric full-duplex, so doesn't these mean ISPs have the same amount of uplink bandwidth to divide between customers as downlink?
a) Most non-fiber connection technologies have limited bandwidth to split between upload and download. If you are offering connections over those, offering a symmetric speed means you are offering a lower max speed (years and years ago, in the single-MBit days, there was a regional German ISP that let you switch your ratio - was very popular with developers and designers at the time, who could reset their connection to be high-upload before sending large files)
b) Only a subset of users cares about high upload speeds (To a degree it's a self-fulfilling prophecy: people are so used to it that most don't even know why they'd want good upstream because they never had the opportunity to do something that would benefit)
c) Some that really want them can be made to pay a lot extra (e.g. for "business class" service, especially if combined with things like static IPs for hosting)
d) some high-bandwidth uses are more likely to cause work for the ISP: people hosting servers (complaints about content etc, attracting attacks), file sharing (rightsholder complaints). Similarly, a customer machine turning into a DDoS traffic source has worse impact if it has high bandwidth
Before cables modems everything was symmetric. Cable modems were bandwidth constrained and they decided to offer more download then upload.
One could also argue that the phone companies as network companies and wanted to make connections and cable companies just wanted to provide content. Offering symmetric bandwidth could be seen as competition by cable companies becuase anyone can publish.
Finally the phone companies started to offer asymmetric bandwidth when DSL was introduced. One could subscribe to asymmetric DSL or symmetric DSL.
Late 1990s V.90 modems were asymmetric, higher download speeds caused upload speed to deteriorate, and often up traffic would be shunted into a more limited analog channel to keep it from interfering with the down speed.
https://en.wikipedia.org/wiki/Modem#Standardized_56k_(V.90/V...
I remember something in the earlier 14400/28800/USRobotics era being asymmetrical too, but can't find a reference.
Where I've lived, ADSL also predates cable modem, and the A there is for Asymmetric.
One component of it can be the exchange and transit deals that the ISPs make. "Peering" is generally made under the terms of "sending as much as you receive", so in that way it can be beneficial to limit your outbound, if you are trying to slip into available inbound bandwidth to pair with some business-class outbound-heavy.
But, there are also lots of other business and technology reasons as others go into here.
GPON has a bunch of modes, some of which are symmetric. Notably a 1.2 Gbit/s down/up setup for gigabit service. Many modes are choosen to be asymmetric, yes, but the technology is not intrinsically one or the other. Notably, just like non-multiple-access fiber connections increasing upstream speed doesn't negatively impact downstream speed (as it does for copper-based connections).
2.4/2.4 is also a standardized GPON speed... Just not very common.
But either way it's irrelevant to the point that the technology can very well support symmetric speeds and offering symmetric doesn't "need a lot of "active" equipment and that drives the costs up." as the commenter I originally replied to claimed. Also evidenced by XGPON having the exact same amount of active equipment.
For what is worth, I haven't had much contact with technology in the last couple of years and things might have changed. My comment was based on my last experience where GPON by design was asymmetric and if you wanted symmetric speeds you would need an MC on both ends of the fiber, hence de "active equipment" need. And then from the MC to a router or whatever you had there.
On the other hand, more than 300Mbps upload is quite ok even with heavy video conferencing and what not.
Because technologies like GPON or HFC were designed with asymmetry in place because most users download much, much more than they upload. In the case of HFC the asymmetry can be particularly egregious.
