My ‘good reason’ is just that it’s super convenient - for backups and painlessly moving apps around between nodes with all their data.
I would run plain LXCs if people nicely packaged up their web apps as LXC templates and made them available on LXCHub for me to run with lxc compose up, but they generally don’t.
I guess another alternate future would be if Proxmox added docker container supervision to their web interface, but you’re still not going to have the self-contained neat snapshot system that includes the data.
In theory you should be able to convert an OCI container layer by layer into an LXC, so I bet there’s projects out there that attempt this.