Just imagine if we said 7man cons lose their snares, or not single but double bar rifles lose their snare. That is way too harsh of a penalty
One is a doctrinal ability that removes every (or most of) weaknesses of a unit, that people use instead of a normal LMG upgrade, and is generally better in every way, so it has to be nerfed in some way, and removing the snare is a good way of telling the player that and LMG is an option, like, reminding him it exists.
Others are non-doctrinal and are purely a choice of a player, that don't exactly make the player go "I will never use any other upgrade, this shit's good".
Even for Rifles you have a Doctrinal 1919 upgrade, which is pretty good, you know? For Soviet Cons you have SVT and PPSH. All these are still good and the player doesn't always choose this, while with 5 men Grens it's a problem.