The last season was full of issues for Tottenham Hotspur and a big title in Europa League that was won in a surprising way does not change this fact. This is part of many reasons why Tottenham Hotspur decided to sack Postecoglu days ago and I think this decision is shocked but reasonable. They need big change at their coach position and even player resource for performing better in a next season.
I am against this decision. I would not be against it if Tottenham management had sacked Postecoglu and selected an experienced coach. Thomas Frank may be talented. But he is not experienced enough. Also his history is not that good.
Tottenham cannot play well in the Premier League. However, becoming the Europa League champion is definitely a great achievement for a team like Tottenham. Since Tottenham management cannot find a very experienced coach, they could have given Postecoglu another season if they wanted.