Dire Bare
Legend
As soon as a RPG setting gets its own novels the novelists will wreck it . . . blah, blah, blah.
Whatever. Obviously there are many who don't feel this way, as the novels sell very well, often better than the RPG property they are based on. How many new Forgotten Realms and Dragonlance RPG books have we gotten in the past several years? How many novels? Certain D&D authors regularly hit the NYT bestsellers list (beyond R.A. Salvatore even).
You seem to have two separate issues, 1) all (or at least most) RPG-based novels are written by hacks, and 2) all (or at least most) RPG-based novels "wreck" the RPG setting.
In regards to the "they're all hacks" claim . . . It's all subjective of course, but the majority of RPG-novels put out by WotC today are of very high quality, with excellent authors. While tastes certainly vary, these books sell well, some authors often hit the NYT bestsellers list, and some of the better authors have developed quite a following. I somehow doubt you have any real experience reading these books beyond a small handful, but even if you've read them all and still think they all suck, you are in a minority.
There are restraints in genre fiction, and there are even more restraints when writing shared-world fiction, but many of WotC's stable of authors manage to quite well within these constraints.
In regards to the "they all wreck the setting" claim . . . . you've got a little more ground here, but still not much IMO. SOME of the various RPG-based novels make major changes to the settings, but most actually DO NOT. Again, you'd know that if you actually had reasonable experience with the many books WotC pumps out each year. And really, even with the famed RSEs (Realm Shaking Events) and their equivalents in other settings, many of them don't really change the setting much either. It's easy to ignore the "Rage of Dragons" event or the "Threat from the Sea" event in your campaign because all you are really missing out on is fighting a bunch of dragons or a bunch of sauhaugin. Some of the events do blow up cities or similar, IMO smaller, changes. Some change the cosmology in a big way, such as the recent Spellplague. But again, if you don't care for it, why does it have to happen in YOUR campaign?
The only RSE that's ever got under my skin was actually in the Dragonlance setting as the cosmology swung back and forth in huge ways three or four times. That planet has a LOT of catacylsms!!!
I've read just about every single TSR and WotC D&D novel released since they started with the original Dragonlance trilogy in the 80s, and while there have been some stinkers (especially in the late 80s and early 90s), the majority of the books are excellent reads.
I put folks who claim (without direct experience, usually) that all RPG-based fiction sucks in the same category as geeks who can't enjoy movies based on any preexisting geek property. Folks who need to relax and enjoy life more, and not get so hung up and overwrought on media they don't care for.
If you hate RPG fiction, then simply don't read it and ignore it! It's pretty easy to do and lots less impactful on your blood pressure! If a RPG sourcebook to your favorite setting includes major changes based on a novel you haven't read (or did read and hated), take the good ideas from the sourcebook and ignore the ones you don't like.