Because rookies are historically poor at developing cars. Grosjean was the best available driver, Gutierrez is a Ferrari driver and Haas is effectively Ferrari B.

I read if he wasn’t going to get a full time F1 seat (he’ll be reserve driver @ Manor), he wanted to make sure he was racing. It’s a good move, I think, but I’d still rather see Rossi along side Grosjean instead of Gutierrez.

Because somebody else paid more money. Sad but true.