If there was a valid reason to write software that efficiently, besides idealism, I'm sure developers would do so. But there isn't in the vast majority of cases, so we don't. iow computing resources are cheaper than labor.
Buying a beefy computer for a developer is cheap, but forcing everyone using your software to default to a 16GB computer isn't. And that's why we get when consumer software takes more ram to run than Windows XP.