Manchester City no longer want to keep Kevin in their club in order to reduce salary cap of the club, and to create space for new and young players joining and growing up. They don't want to build up their squad around an old player like Kevin but if they don't have too bad performances in this season and their finance was not afffected too much, they might use Kevin as a substitution and he surely will make good contributions for the club.
Unfortunately the big decision was made weeks ago, and Kevin will play his last matches for Manchester City before his departure. He will be missed by Manchester City fans after all amazing goals, assists and moments he has shown in about one decade.
I believe KDB age is not the main reason City opt on not renewing his contract but rather his injury records in recent seasons has been poor. Now that they are working on rebuilding the squad after a somewhat of disappointing season, this is fairly the right call.
Florian Wirtz is quite expensive, about 120-150 Million Euro, so if we talk about money, the city will require a lot of Money to recruit him, and it's not so efficient when I compare to keep KDB on the club. We haven't talked yet about Florian Wirtz's salary, which I think would be higher than KDB's.
His injury record is among the key reason the club would want to bid him goodbye now. Also, Florian Wirtz is a good buy and definitely they would pay more to get him and his pay may be quite high but not as KDB who is currently receiving £400,000 weekly, excluding bonuses
https://www.capology.com/player/kevin-de-bruyne-33417/Also, you speak as if City would be able to a class like KDB to replace him now, Florian Wirtz is still good and can get the job done but not as well as KDB. Anyway, he is young and just turned 23 today, he is a good buy and a good potential replacement for KDB at City, if he continue with his growth/fine form but that is if City can beat Bayern Munich for their signature.