I think it's both. Ten-year-old enterprise desktop applications may be functional and even highly usable, but they look and feel ancient. It's been a long time, but I remember using Windows software in the 2000s where I could almost smell the mold and dust. Applications like that are the software equivalent of Miss Havisham's wedding dress. If you're positioning yourself as a fashion-conscious brand selling products that become part of a person's identity, it helps to have a mechanism for sloughing off applications that aren't constantly being refreshed and rewritten. Constant rewrites aren't economical for enterprise applications with a few hundred or few thousand users, but those have moved to the web anyway.

Note that this doesn't reflect my personal values about software, but I can see how it serves Apple's priorities and keeps their products attractive in the eyes of their customers.