Why am I not getting any better at push-ups?

I posted before that I have been getting back into a fitness routine in the last few months. My focus has been on building muscle and strength. This is a relatively new approach, for me, as my fitness “history” was always focused on cardio, I was always big on running, and most of my strength training came from yoga and light weights (I’m female and the conventional advice for a long time was light weights lots of reps.)
I’ve seen steady progress in everything that I’ve been doing, I’m able to lift much heavier weights than when I began, I went from doing a handful of bodyweight squats to hundreds, or being able to add and increase weight, everything is going as expected… except for push ups. I am still stuck on an incline push up (one stair), and I can still only do about ten, ten, before I’m shaking and losing my form. My form is good to begin with, elbows close to the body, hands wide, I’m not relying on gravity to do the work, I just can’t seem to get any better. What gives? How do I get over this hump?