why do my guinea pigs keep dying

i feel like no matter what i do they always just end up passing away.

i had a pair of two year old boars and a pair of one year old sows but in february one of the boys died seemingly randomly so a few weeks later i got a new friend for the one i had left. then, the new one ended up passing away on christmas even so i decided that i didn’t want to keep replacing them bc it’s pretty heartbreaking so i rehomed my last boy to someone with other pigs for him. then today, one of my girls died.

i do everything that people say you’re supposed to do. they live in a cage above the minimum size on fleece that i clean regularly, they have a constant supply of hay, good pellets, vitamin c, vet care, but i feel like it doesn’t matter because they just end up dying. when they die it seems to come out of nowhere and i just find them laying there. is this just part of having guinea pigs? is there anything i can do? it’s honestly just really disheartening to put so much care and effort and money into them just to have them pass away in such a short time.