The season hasn't started yet and he may have started making statements to the press early. I hope it's not the same as when he was at Manchester United, where he started with losses in friendlies and then came his interviews in which he complained about players and the relationship with the players became terrible, then he made terrible signings.
Now at Leverkusen, he already had a defeat in which he conceded 5 goals in the friendly match. In 5 days, he will have another friendly match against Bochum, who were recently relegated from the Bundesliga. If he loses, it will be terrible for him.
Getting flogged by Flamengo U21 a few days ago was just a prelude of what is to come. Xhaka knows Leverkusen is finished with ETH at the club, and that's why he wants out before it's too late. Another thing is that he's not fighting to move to a bigger club, as most players would do. He's fighting to go to Sunderland, which Leverkusen is obviously bigger than. That tells me he's desperate about leaving and does not want to stick around when the ship starts sinking.
He appears to have completed his goals with Leverkusen, and it's not easy to earn a Premier League transfer at his age. Having achieved this, he wants the transfer to happen as soon as possible. At 32, he has the chance to compete in the Premier League. Sunderland seems like an opportunity for him, but perhaps Bayer Leverkusen will be a serious title contender this year, just like in previous years. In that case, he might regret leaving the club.