It seems that Google wants to make using app bundles a requirement for new apps on Google Play in 2021: https://www.youtube.com/watch?time_continue=320&v=cMr-b660Esw
This would mean developers have to upload their signing keys to google play even though there's no technical benefit in doing that. You can achieve the same efficient download sizes by using bundletool locally and uploading all generated apks. But it seems google will stop allowing that and just wants your signing keys.