Not the ego as much as pure greed. There is a strong financial incentive to repackage a software every so often and sell it again for full price/sub to the same people who bought it before. For example full price single purchase apps on the mobile are going away slowly. Older purchases are silently deprecated or disabled or have ads injected, and instead new versions are promoted which are now not an update but a separate app with the same name and functions, you just need to pay for it again.

I'm thinking that the age of app compatibility will end in 10-20 years, and there won't be suh a thing as "old code" because it won't run at all on the new hardware or OS.