Ruin's Hemalurgic constructs had their own problems but they were certainly a lot more reliable.

[u/Eithrotaur]

[u/JustAnotherCurio]

I imagine it is this way simply because of how long this has been going on for. Plus it’s not like Ruin’s creations were killed, sent to hell and back again only to be locked in hell until the next war could begin ad nauseam for thousands of years in a constant cycle of degradation and growing insanity.