Microsofts failure in mobile has simply been due to the fact that they weren't able to excite users with hardware. This changed with the Surface line.
But as far as the Surface. MS only made $1.329 billion on Surface devices. That’s less than a third of what Apple makes on Macs. Heck that’s less than Apple makes on Watches and AirPods.
https://sixcolors.com/post/2019/10/apple-results-64b-in-reve...
https://www.techradar.com/news/microsofts-surface-sales-keep...