Part of the issue is this affects different countries differently, based on residential IP allocations to household ratios. I am currently on CGNAT in Australia split 256 ways, and any site that doesn't support IPv6 can be borderline unusable. I can't imagine what it's like in countries with worse ratios, like India.
It's been in crisis for decades, but it's also getting increasingly worse every year.
I feel this issue has started to slowly become worse and worse as we've been able to build better "preference profiles" based on small amounts of data. I notice it often when watching a single YouTube video in incognito mode, the sidebar is usually full of fairly racist Australian content (I am Australian). This is something I would never normally see, and not something that's likely coming from whatever video I've decided to watch in incognito. It's likely just assuming based on what's a common trend in my location.
If an algorithm knows you well, it's usually pretty okay, but until that point you're being bombarded with lowest common denominator content based on your demographic. Shorts seems to be even worse; mine is mostly science facts and comedy skits, I didn't understand the "brainrot" descriptions until I looked at a few in incognito mode.
I'm not very familiar with men's fashion so I might be wrong. My understanding is that a lot of the time, size is _not_ about how tall most tops are, it's about how much horizontal space it has.
As a 5'10" woman, I do find it oddly convenient a lot of the time as that's seemingly the height of 99% of models, however everyone has different body proportions so it doesn't end up being a super useful metric.
Leg to body ratio can differ greatly, and when buying tops you can really only compare the fit with people who have a similar torso length than you. No clothing site is going to start listing individual measurements of their models like that, so it'll always be a vague guide.
I actually spoke to someone a few years ago who worked in marketing at a US clothing manufacturer (I'm Australian so not sure how well it applies to my own experiences), but apparently many stores are trying to encourage a small portion of returns of online orders because many people end up buying more items in the process.
My personal theory here, is that sites are just trying to let people know that a model is wearing their clothes. It's not to help gauge sizing, it's to let you know that person is _really_ a model. Models are often tall and slender, so they want you to know that tall and slender people look good in their clothes. The effect of "If an attractive model would wear this clothing, you can look like a model by doing it too!"
It's been in crisis for decades, but it's also getting increasingly worse every year.