FEMA didn't go cheap, the manufacturer did. The government is not legally allowed to manufacture it's own stuff. They have to put out a request and allow everyone to bid on it, then they take the lowest bid offer. The manufacturer then cuts corners wherever possible because that is how they maximize profit, and the quality does not matter. Once they win the contract whatever they deliver that is technically within the requirements of the bid has to be accepted.

FEMA most likely paid several times more than those trailers would sell on the open market.