It's all about better tracking. I'm not quite sure what additional info they get exactly, but tons and tons of mobile websites (that work and don't get deleted) are close to unusable due to a barrage of popups telling you to use the app (e.g. Reddit and other socials).
Also there is no indication they will stop the mobile web version. Already today the mobile web version is there but it explicitly refuses to show the boarding pass QR code: https://i.redd.it/lj3wdnfp9mq91.jpg