Uh, have you ever seen the length of a typical STM32 errata sheet? ;)
For ST it could be that they seem to be the most popular cheap ARM microcontrollers for hobbyists and consumer products, so it's easier to find faults in them since so many companies use them, similar how the most used pieces of software also have the most vulnerabilities reported on them.
Also, maybe ST was not a great example on my end, as they seem to have an obsession lately with outsourcing and farming out everything to the cheapest offshore location possible and penny pinching to the extreme for their consumer oriented parts. I don't blame them though, competition in the generic ARM microcontroller market is cutthroats and margins are slim and salaries are low and your major customers (Sony, Apple, Samsung, LG, etc) keep putting the pressure on you to lower your prices or threaten to look somewhere else.
One fun one was that when accessing the External Memory Interface module (think: parallel ROM) and switching from Bank 1 to Bank 0, the HDMI controller would get reset, but only when configured for two banks of 32 MB.
If I did one bank of 64 MB and just used the extra pin as CS, it worked just fine.
There are lots of similar quirks in every chip.
Are you some hobbyist or small company who sent your issue report to some generic company email address? Then your report most likely neve reached anyone on the team working on that chip, but probably reached some clueless jobsworth who didn't know what to do with it because large semi companies are highly siloed and there's no centralized management for such things, so you need direct contact with the team responsible for that chip.
If you're large customer, you then have direct email addresses of support engineers, application engineers and the engineers who worked on the chip itself, and so your reports will definitely taken seriously.
There's also another issue. There's public datasheets and eratas which are often not updated or fully transparent, and then there's confidential datasheets and eratas, which are updated and issued under NDA to industrial customers on a need to know basis. As a hobbyist you rarely get all the truthful info.
It's not ideal, but the semi industry mostly focuses on large customers who buy in large volumes of product, not on hobbyists and tinkerers.
Some die photos here: https://mecrisp-stellaris-folkdoc.sourceforge.io/clones-stm3...