Lopetegui's, first team professional management career, was lasting 10 matches in the Spanish Second division, with Rayo Vallecano way back in 2003. He was sacked after 10 matches. He didn't manage another first team football club until he got the sack at Porto earlier this year. He managed Real Madrid B, that's it. His only achievements are with the Spanish under 21 and 19's. As you know, Spain are blessed with young talent.
I can't see how, if your objective is to get promoted from the English championship, win the PL and win the European cup, you would employ Julen Lopetegui. If you want to become a feeder club and develope young players, given to you by Mendes, to then sell on as a profit, it makes perfect sense.