I always though the poor reputation of Italian milsurps was due to the poor performance of Il Duce's forces in WWII, not to flaws in design or manufacture. It's our own beloved M1903 that has a reputation for blowing up.
it's a number of reasons.
1. the bore diameters vary greatly, some are undersized, some are way oversized.
2. they are the only front line battle rifle that still used en blocs by the beginning of WWII.
3. generally poor condition wood though there are plenty like mad crate builder's that have good wood on them, must be an issue with how they were stored.
4. probably the big one is when all these rifles were coming over as surplus a little man named lee harvey oswald decided to put a carcano to use.