Not having seen you ski, I have a couple guesses.
I feel like I cheat a step going edge to edge somehow. When I try to do it going slow, it's almost worse.
The step that you may be cheating as you go edge to edge is a flat ski. Have you heard of 2-4-2? When turning you're on 2 edges, then the ski is flat with 4 edges on the snow, then the opposite 2 edges. This flat ski portion of the turn is always there, but in fast skiing it can be nearly imperceptible. When skiing slowly this 4 edges flat ski segment of a turn can feel ridiculously long as you ever so gently roll from 2 edges to a flat ski and over to the other 2 edges.
Another piece that is commonly missing when people try rolling from edge to edge is ankle flex. In bare feet stand up straight and try to roll your feet from edge to edge, left big toe and right little toe to left little toe and right big toe. Next flex your ankles so your knees are over your toes and roll from edge to edge. Which works better?
A third common issue going edge to edge is too much tip lead. Play with your tip lead while standing across the slope. How does edging feel when your feet are next to each other, when the uphill foot is a little bit ahead of the downhill foot, and when the uphill foot is far ahead of the downhill foot. You'll find a little tip lead allows you to get on your edges much more comfortably because the ergonomics just work better. Too much tip lead and your uphill ankle opens and you can't get on the edge of that uphill ski. Sideslip, stop, repeat.
Stance width can also be an issue. Try the same sideslipping exercise varying the width of your stance. How does edging work when your feet are right together, hip width, and far apart? I bet roughly hip width will allow your ankles and knees to roll together best.
Does any of this seem likely to you?
And, of course, how do your boots fit