Alonso want to stay but Alpine didn't want him for as long so he wanted to stay so he cut himself a better deal with Aston Martin
https://www.bbc.co.uk/sport/formula1/62389741
I've read Alpine's option on Piastri ran out the day before the shock Alonso announcement from Aston Martin. If so, Piastri is now a free agent, he knows McLaren are wanting to replace Ricciardo so he must be exploring this option or a deal has already been done
To add more intrigue, Alonso and Mark Webber are friends, Mark Webber is Piastri's manager so I'm sure they will have talked before the musical chairs kicked off
I've also read that Schumacher is out of Haas, if this is true does it mean Herta will replace him as he would seem the ideal fit for the team?