It's about your users, not your developers. Of course it costs more to provide a better product, which was the original reasoning behind providing native desktop applications.
What they're doing now has more to do with politics and skillsets amongst traditionally web-focused engineering management and teams, than it does with actually creating a great product. Spotify has a ridiculously hard time hiring outside their management's core competency of web-focused development, including both for mobile and desktop. That has more to do with their management than the job market, though.
As an aside, I can't say I understand why web developers find it so impossible to migrate to mobile/desktop. Time and time again we work with organizations who have built a large server-side web-focused team and somehow simply cannot manage to support the mobile/desktop. What kinds of engineers are they hiring that they can't learn a new platform?