Personally, there are some things I have found difficult to do (getting a chat going with a customer service agent) and some things that are very easy (checkout process, making a return). It's no surprise to me that they would make it slightly more difficult to find a live person to chat with since they probably want me to exhaust the other automated methods of solving my problem before doing that. Is that bad UX? I don't think so.
NNG often say to follow conventions and Amazon has been leader for so long now that I can't help but think they have established many conventions now that might have been viewed negatively 16 years ago.
Ahh, you want "clean" design where maybe there is just one box with beautiful font and not all these options "cluttering" things. You want those options buried in an option tree maybe 8 levels deep.
Well, I'm pretty sick of this minimalist design philosophy that requires 10x more clicks to accomplish anything because a designer decided the original was just too easy to use and wasn't "engaging enough" to generate enough clicks. They have made the web a much worse place for getting stuff done online, and it's no wonder that Amazon, the home of one-click purchasing, has continued optimizing for having the UI get out of your way and accomplish the most with the least effort rather than building attention-seeking UI "experiences" that require lots of interactivity to get simple things done.
And AWS.
The web store UX has become appallingly bad - unreliable/fake reviews, tens/hundreds of sellers all roboselling the same identical items from China, poor quality items, unreliable/poor product search ("10TB external hard drive" shows... not many 10TB external hard drives). And so on.
Amazon is commercially successful but few would argue their UX is good.