You usually stop doing something when it's finished. That's kind of the idea, Jesus said some words when he died. He said it is finished.
I know it's impossible for you to understand that those feast days had specific instructions given by God. Those instructions included the high priest making sacrifices, and making offerings to God. Those feasts were the eating of the sacrificed and offered food items. If you don't do those prescribed ordinances by God, you aren't keeping the feasts. Jesus is the high priest and has made the final sacrifice. There is no sacrifices left, there is no temple, so there is no feasts, but the one that our high priest has given us. His body as bread, his blood as wine, at the new temple which he has given us, our own bodies, and our holy convocations which is his church built upon the rock of the revelation that He is.