I suppose maybe the cable networks are more optimized for average user behaviour (far more download than upload), but maybe there's also a fundamental limitation with the cable infrastructure that prevents faster uploads, perhaps to do with cable's legacy delivering television broadcasts? Whereas with fibre, almost everything I've seen available comes with symmetric speeds by default.
However, there was a technical issue I had some months ago with a faulty Arris modem provisioning file that disabled upstream bonding across most of their models. It took an email to the CEO to sort it out (after a Reddit and DSLReports post on the matter).
Previously I had been on a 50/10 tier and when the new business class tiers were released they blamed my trusted old SB6121s for being too old, so I bought 2 newer ones in the SB series and had same issues. After writing the CEO and CC'ing all the techs I spoke to and including links to the threads they gave me a direct engineering contact that confirmed the issue. For the trouble they credited me out 2 months of service.
DOCSIS 3.0 (I think that's the latest) allocates a particular ratio of download vs upload frequencies, so even when speeds increase the asymmetry is still the same. I heard the next version of DOCSIS might change that though. Ideally there'd be enough fiber to not require DOCSIS anyway, but I don't have my hopes up for that.
Hopefully with a lot more WFH arrangements people start demanding symmetric connections. But
Anything more than that, especially in gigabit range is just gimmicks, IMO.