Allegri has only been away for around 18 months, not too dissimilar from Pochettino and people wanted Pochettino. It's not like football has drastically changed either. Plus, he has been learning English ever since he left Juventus and there have been reports saying that he wants his next job to be in the Premier League.
I wouldn't mind Allegri, if only because he is a tactically flexible manager. Otherwise, I have my doubts about his playing style and it suiting this team. But hey, surely he'll make us play something more attractive than spamming crosses into the box, right?