@pablob Like many others have said, it sounds like you need to focus on them more and push (safely) into failure with them. I’ve learned its better to fight the weight all the way down and not just drop it, you’re still working the muscle.
Part of it could be genetics or how you’ve naturally used your body over the years. Just means you have to try harder. And again, do it safely, slowly over time and consistently.
I actually had the reverse problem when training, I could build up to 50 full pull ups per workout, usually hitting about 5-10 if I hadn’t been training. But my shoulders and back are more naturally stronger for some reason. Plus I am lean, 6’ @ 160lbs but was 6’ @ 140 for years due to years of cross country and track, and again, genetics. But ask me to do a push up and I would struggle harder, my chest is naturally more weak.
Keep at it, go slow, isolate the areas more and fight it all the way down (and up!)