Non tech-oriented people, the masses, absolutely love customizability and malleability--but aren't willing to handle the responsibility. They will reach out to tech support who can't possibly know every customization option of every application and its effects, and complain when they tell them to reset/reinstall.

And in a corporate environment where the company provides the PC, the company would rather not deal with it. Office dominates at the workplace, is mostly making money from corporate users, and users want it to behave the same way it does in the workplace. So any backlash by users is simply not going to matter unless it might cause companies to not renew their licenses.

A company I work for is moving to Office-on-the-web for PCs that are used by people who don't really use Office that much except possibly to read Word docs, in order to save on licensing costs I presume. It's even less customizable than any desktop version. So the trend is going to continue.