The problem is it doesn't take much for people to get burned.
Quick example: I was looking for some resources for running an adventure in Souragne in Ravenloft (a domain that is very styled in New Orleans/Southern Gothic/Voodoo). Looking to save some work, I Googles "5e voodoo adventures" and eventually stumbled across one that sounded interesting. It was cheap ($5) and I bought it. I promised new magic items, an adventure, and a "voodoo queen" class for NPCs.
It was bullocks. The module itself was bare bones with a plot that is literally spelled out in the opening text block. I've seen MMO fetch quests with better structure. The NPC class was basically "add the wizard spellcasting progression to the character" with no class features or abilities. The magic items were trash, the new spells were clearly imported from Pathfinder without thought (including spell effect scaling by caster level not spell level) and the whole thing was padded out (they gave a recipe for food to serve during the game!). The art in was nice for 3d rendered (not AI) but that was all it had.
I didn't expect much, and I was still disappointed. And I wish I could say that was a one-off, but I've seen my share of bad products in terms of balance, design, or functionality to the point that, unless it comes from a major publisher I trust, I expect it to be amateurish, broken, and will need to be reworked to be functional. I completely get why it has the reputation it has, and its VERY hard to separate the wheat from the chaff.
The product wasn't DM's Guild, btw. It was some small studio I'm convinced was one guy using his blog to sell stuff.