See, there are lots of suppressors out there that are constructed largely of aluminum and intended for use with .22LR ammunition. While classic deuce-deuce operates at higher pressures than most people realize, it's still a very small case capacity and doesn't produce a lot of gas. An out-of-battery discharge with a .22LR rifle is startling, but not the sort of thing that wrecks guns and removes digits*.
5.7x28mm operates at double the chamber pressures and also has better than double the powder charge of the classic rimfire round. That's a lot more gas to handle and it can make a little alloy rimfire can look like the exploding cigar from a Bugs Bunny cartoon.
*Incidentally, this is the reason for the dearth of straight blowback semiautomatic rifles chambered in .22WMR. It operates at similar pressures to .22LR but has better than double the powder charge, so an out of battery discharge is a much bigger deal. People tend to be pretty lackadaisical about cleaning rimfire rifles and fond of doing mag dumps with them and, well...
