You're probably over-cleaning.
If you're cleaning it hard enough to remove the brown/black layers that form near the bottom - you're cleaning way too much, and never letting it build up a layer of seasoning.
Despite the claims that modern soap won't hurt, I find it varies tremendously by brand. So I don't use it.
I literally just drop about a tablespoon of salt into the large skillets, and wipe out with a paper towel while it's hot still.
The egg pan gets a light scrub with a non-scratch sponge, and that's basically it.
Also - I'm in no way affiliated, but this is basically the best cleaner for cast iron you can get: https://www.amazon.com/Ringer-Original-Stainless-Cleaner-Pat...