1. Proxmox cannot even join a network using DHCP requiring manual IP configuration.
2. Disk encryption is a hell instead of checkbox in installer
3. Wi-Fi - no luck (rarely used for real servers, but frequently for r&d racks)
Of course, it is a Debian core underneath and a lot of things are possible given enough time and persistence, but other solutions have them out of the box.
Proxmox wasn’t considered because of the audience (leadership) and Proxmox’s perceived market (SMBs/homelabs). I couldn’t even get them to take Virtuozzo seriously, so Proxmox was entirely a non-starter, unfortunately.
FWIW, I use Proxmox at home. It’s a bit obtuse at times, but it runs like a champ on my N100-based NUCs.