What makes you think it's not a strength thing? Doing a push up on your knees gives you a much shorter level to work from and therefore makes the movement easier. Same as doing bench dips with your legs straight or knees bent - knees bent puts your point of contact closer to you/the bench, giving you a shorter lever and an easier movement.

Try doing full push ups without going full depth. So stay on your toes, but use an ab mat or a couple of bumper plates as a depth marker. Hit the marker each time, making sure it's still difficult but doable, and that should help to build up your strength in that movement and with the body position. Over time you can use a smaller depth marker until you've built up to hitting the floor for full depth.

Also, be careful with doing 'wormy' push ups as it can put a lot of unwanted strain on your lower back. You'd be better off doing them half-depth but keeping your back straight and core tight.

Btw, that's how I had to start out too. I could do like 1 real pushup, but for a wod would do them at an incline. Now I can do 30 strict pushups unbroken!