Because of forum posts like this, which might deter "idiots like me" from buying from them, and maybe a few class actions... However, they are always welcome to fix their problems if they really want to...
Are they really that bad? I mean it sucks USA doesn't design/build too, but I just ordered my first two S9s. I assume most have a good experience or they would not stay in business. Plus, I have an S3 that claims to have 1100 days of activity clocked.
S9s are not awful. But you are more likely to have an issue with one than with an S7 or S5. Neither of which will do much for you now. And the S9 is the most expensive miner this late in it's product stage. I think part of the reason people get pissy about breakdowns is the poor repair options and loss of mining time. Not to mention the virtual monopoly Bitmain enjoys.
In my opinion, we are lucky to have anyone selling us miners the way btc mining has gone all corporate.