In the bull run, the market captures positive news and ignores small negative news. When people starts selling to make profits, the prices goes down and every negative news are highlighted which can lead a crash.
Market Needs Crash
I think saying something "needs" a crash is a fallacious argument. Nothing is due a crash. In ideal situations, bitcoin could potentially just end up constantly going up. However, we do not live in an ideal situation. However, again, this does not support the cause for having a crash. Again, I'm not saying that there aren't going to be any crashes, but that your logic is partly fallacious.