The technical reason is that by restricting upload speed they can offer a higher download speed, and that is what most users care about.

I find that reasoning suspicious. Ever notice how most of the muni and coop internet providers offer a symmetrical speed while att and comcast don't? My bet is that there's no real technical limitation, it's simply price segmentation.

Fiber is symmetric, coax is not. This isn't some grand conspiracy, just how the underlying engineering works.

In the UK, Openreach FTTP is heavily asymmetric. Network operators aren't entirely at the whims of asymmetric standards: network operators want asymmetric services.

AT&T does offer symmetrical speeds. Most PON-based FTTH ISPs I've encountered do.

There are technical reasons for offering asymmetrical speeds when it comes to coax connections. There's only so many channels on the wire, a lot are still dedicated to television, people mostly only care about download, so they prioritize it. PONs don't carry television and are just fundamentally different in design, so its easier for them to support symmetrical bandwidth.

There is a technical limitation on cable and DSL networks but not on other techs like fiber or wireless.

This is nonsense. Fiber cables are always capable of the same speed in both directions at once. The actual reason is so they can sell you an overpriced "business" plan if you need upload speeds from the current decade.

A very small part of the country is connected by fiber, and fiber connections are always symmetrical. The vast majority of consumers still get internet via coax cables, and bandwidth is very much an issue on those.

No, a very small part of the last mile is connected by fiber. Trunking is always fiber these days. As are local neighbourhood branch points, if your provider evolved from a telephone company. (If you live in an apartment building served by an ex-telephone ISP, you likely have fiber run all the way to the network closet of your building, with only the per-subscriber in-wall wiring switching over to copper.)

ISPs that evolved from cable companies might still be using cable hubs with a common collision domain, but only a relatively small number of subscribers will be riding the same copper — it’s just cheaper these days to convert the signal to fiber as early in the signal path as possible. Plastic wires are cheaper than metal wires, and you need fewer of them (and so fewer switches.)

Yes, *fiber* can. But the majority of Americans use Cable/HFC (DOCSIS) technologies. These were designed as a one-to-many closed loop TV broadcast on a coax line. Except with the incoming DOCSIS 4.0 deployments it's always been asymmetric as a limitation of the technology

Fiber is not ubiquitous. Many of us are still on DOCSIS over copper, in which case the person you are replying to is exactly correct: upload speed can be reduced for additional download speed.

Though the fiber system as a whole may not be capable of symmetry. For example GPON with 2.5gbps/1.25gbps up/down and 10G-PON at 10/2.5 up/down.

True FTTH is naturally symmetric; PON is not nor is Cable.

Assuming we are talking about Cable internet: If they were starting from scratch all possibilities are equally expensive, but they have installed equipment in your neighborhood which assumes a specific channel allocation.

They have increased the channel allocation for upstream in recent years and DOCSIS 4.0 allows symmetric connections, but the demand is for downstream, and the fewer channels they allocate to upstream the bigger number they can advertise.

It depends on the layer 1 medium. In a shared RF environment (dialup, cable, wifi, p2p RF) you normally have a shared bandwidth space. This is typically "channelized" and you can pick how many channels you want for "up" and how many for "down". This isn't normally dynamic, it needs to be fixed by the standard or at the very least by the head end equipment. It's more expensive in the above RF spaces because cabling is expensive the more home runs you want to do. With fiber it's a little easier, 1:32 pon splits still give a _lot_ of bandwidth for upstream because it's easier to isolate the adjacent wavelengths (you can pack them in tighter), and the normal noise floor is lower. With 1:1 fiber DIA it's a total non issue and you can do what ever is the limit of the noise of the fiber and the limits of the transceivers (typically optical packages in sfp/sfp+ packaging these days)

AFAIK, PON (Passive Optical Network) has inherent reasons to be asymetric

Not really. I'm sure asymmetric PON is cheaper but there are plenty of symmetric EPON modes.

My assumption is torrents are a threat to streaming services already and potentially a death blow if uplink speeds are too fast.

why would uplink speeds being fast contribute to torrents outside of the first few seeders?... you would just have more peers contributing smaller amounts

When I worked at a small ISP, this was indeed a threat. We offered symmetric speeds though and dealt with it via traffic shaping.

It really was just the odd teenager torrenting here and there.

Also new media (streamers and tubers) rely on uploads and are eating cable’s lunch. It’s just extortion through monopoly.