WotCs could place crisp $20 bills in the back of each book and people would complain it's not a $50.
Then again, I'm increasingly convinced fandom is a net negative for any given franchise. I've yet to meet a a fandom that isn't overwhelmingly critical of the thing they claim to enjoy. Things are always better before, the franchise is always dying, the current owners are incompetent/greedy/hateful and it's the burden of the True Fans to save the franchise from the casuals who are watering it down.
I think the Internet has solidified what petty, vindictive and unsatisfied people the world is really full of.
We would complain that it's a $20 bill and not a Euro bill or a British bill...

Not that I buy physical books anymore...
As someone else already mentioned, slightly annoyed, slightly happy or even happy people will often just not comment. And when people are negative, they are often negative about different things. The people that are complaining about 'all the negativity' don't realize that they can't tell the difference between different negativity or the different personalities that spout negativity, they just perceive it as a big nasty miasma, while it isn't.
I'm not exactly happy about the art in the D&D 5e 2024 books. I'm overall very happy with the 2024 rulesset, except I'm extremely disappointed about the inconsistent cohesion of those rules (see the stealth discussions from last year as an example). I had expected better from WotC/D&D for a rules set that's
not a new edition, but a revision... That said, I've lived with 35 years of TSR/WotC and Games Workshop rules, so I can take quite a lot of that...
As WotC has decided that they won't sell us pdfs of the 5e books, and there's only a little actually available officially for 5e on FVTT, I'm not buying all that much anyway. And what I'm buying is only $30 per product. I haven't seen an image from the PHB and DMG for a LONG time, as I only own the FVTT versions of that and all of the rules/abilities come without any images. The images are there, I just don't need to access the sections that contain the artwork I don't like. I think the only thing I really see regularly is the art for the items and the monsters. We recently fought a Beholder and I dislike the new Beholder art, I wasn't DMing at the time, but I could easily use other artwork in FVTT for tokens and the full image. The art for Pandelver and Below and Tomb of Annihilation was good enough imho, as what I saw of the Vecna adventure (a friend owns the book and I started to convert it for FVTT).
Was all the art from 35 years ago great? Heck no! there was a lot of Line art in 2e, not all of which was pretty, but that often meant that more attention was given to the full page spreads, of those I didn't like, I could appreciate. A lot of the 3e illustration style I did like, of course, not everything, but enough. Not really so of the 5e 2024 books, but I occasionally do like something a LOT, like the recent Dragon Delves Alt Cover by Justine Jones.
With the current use of VTTs and specifically FVTT, I can far easier ignore, remove, or even replace RPG art in my game/rule book. I could shut my trap as it's not really adversely affecting me anymore compared back when I was still buying physical D&D books. But, as I'll probably be paying for it anyway (or not), why can't I express my opinion? Just because it's not what you want to hear? There comes a time when you have to say, what WotC is producing with D&D is not for me anymore, and I've done that with a LOT of D&D 5e (last physical books I bought for D&D were the PHB/DMG/MM 2014). Heck, I'm a big Planescape and Spelljammer fan, but didn't pick up the 5e versions after all the hub-hub. It's that the actual content of some of the books we can actually live with, otherwise I expect we would have moved on to Pathfinder 2e, last year that was a real possibility (I already bought the pdfs for that), but most of the group grew enthiousiastic about D&D 2024 and here we are now... And to date we've been using the Forgotten Realms we know of from 2e/3e with just some online updates to the current timeline, heck even the maps of FR and the cities we visit come from previous editions (Mike Schley).
For many of us, it's a check of "Am I the weird one?". Which is probably the case, but luckily we aren't alone. You can't please everyone, but I think that the current illustration style is due to an attempt to please everyone...
Some things were better before, not everything. Not every change is a positive one. And there are still people who hated 3e and hate 5e, while prefering 2e or even D&D Basic. They often have made 'peace' with that reality decades ago. Some of us are still balancing on the "Do I even want to play this version of D&D?". There are still things that attract us to this version of D&D, just not everything. And a major disconnect between the illustration style and the user, has a huge impact if that player/DM had to physically page through books with art they hate all the time. It's not so bad if you don't 'care' for it, but it's bad if you actively hate it. I think i would be at the point where I would actually would make/print my own version of the books if we were playing in person without a computer/FVTT.