Huge pages need contiguous free physical pages. Without preallocating them at boot time, with higher system uptime, chances of finding such region to satisfy the allocation are slimmer, especially for 1G pages, to the point when even services starting later at boot time might not get them due to external fragmentation caused by 4k pages allocations.

While I can see why special permissions are needed to grab them, the whole filesystem thingy is clunky as hell. I have no idea why they didn't put them by default in /sys or /proc.