The weird thing about this is that the only company I've seen doing problematic user-agent handling in recent years is Google themselves. They have released several products as Chrome-only, which then turned out to work fine in every other browser if they just pretended to be Chrome through the user agent. Same with their search pages, which on mobile were very bad in every non-Chrome browser purely based on user age…
I frequently consume web articles with a combination of newsboat + Lynx, and it's astounding how many websites throw up HTTP 403 messages when I try to open a link. They're obviously sniffing my user agent because if I blank out the string (more accurately, just the 'libwww-FM' part, then the site will show me the correct page.
I'm pretty sure that the webmasters responsible for this are using user agent string blocking as a naive attempt to block bots from scraping their site, but that assumes that the bots that they want to block actually send an accurate user agent string the first place.