Knives that don't stick are definitely the exception; that's why discussions like this even exist.
You can imagine that a knife made of ordinary window glass would stick to things VERY badly. That's part of the problem - shiny, perfect, non-porous surfaces really stick. Another part is we don't know the magic formula of what kind of imperfection and what kind of porousness will really fix that AND are not too difficult to create on a steel blade. And another part is that's probably not the entire story. We know a mirror polished thin flat blade is always sticky as hell, but we haven't figured out the truly effective ways of roughing it up, making it bumpy, making it "just not shiny", punching holes in it, etc etc, to really make it work. There's a lot of guessing and a lot of giving up.
One pretty helpful trick that we don't like for obvious reasons: irregularly serrate and roughen the
edge of the blade, making the sliced food rough and irregular and therefore less sticky.
Another unpopular solution: Get used to stuff sticking to the knife.