What I'm seeing here is that the player have found that you are predictable. They know it poses them no danger to blow their load every fight and not be afraid of having nothing else to do. This is about you as a GM needing to push variety in encounter frequency and throw them a curve ball occasionally.

I get where you are coming from with APs I've run quite a few and frankly yes the amount of combats can be a bit much, but I think in addition to what others have said it's nice to give the PCs an easy encounter here and there especially if it's against things they have fought before as an opportunity to show them how much more powerful they have become. You say you've cut like 80% of encounter that seems exceedingly excessive IMO I might look for a better balance of like 50% if you feel like combats need to be cut or combined.