I don't know what he was thinking, but this midfielder has actually done quite well at Manchester City and this season he has participated in defending Manchester City to win several titles.
With his transfer I'm not sure he can develop there like he did with Manchester City.
Or could there be a tempting offer from Barcelona so he chose to go there instead of playing with Manchester City, who are now kings in the Premier League.
ilkay Gundogan is an old player and he is 32 right now that's why there is maybe not be many teams that want to hire this player, Gundogan had a good performance in Manchester City and he is an important player there, but the offers he got from Arsenal and PSG can't change anything for him because he can get all he wants to get in Macnshter City and with a coach like Guardiola he can achieve the title he wants to earn.
Even if he joins other teams and accepts the other offers there is no guarantee to say he can have a good performance in these teams that's why maybe staying in Manchester City could be the best he can do.