Their capital growth comes from their reputation. Just about everyone who has ever used a zip file knows about WinZip. The average computer user (the one who usually doesn't search for cracks or even knows about them) will think of WinZip when he requires a nice full featured program to handle zip files. Also knowing that he will not have to pay again when they release a new version is a big selling point. Imagine how many people would love Microsoft if they employed this policy

Also those people who use cracks will almost certainly look for a new crack if the protection is updated, in which case it's still pointless for the company to update the protection