Happ very well could have had a nagging injury that needed a break, too. TT's point is that the manager has access to a lot of information that we don't. Without that info, the decisions can look bad from the outside.
Also, while LF in Houston is funky, it's small. There's a fair probability that none of the quirks come into play and it's a good place to put a bad fielder. Plus it isn't like Morel hasn't played the OF at all.