I am not sure if I understand your meaning, might be language barrier here?
Do you mean to say that in the Windows application store there is better range of applications than in the Jolla store?

I have actually not found that to be true. I only have some applications that I really need badly, and one of those is for example the Jolla native "Working Hours Tracker" which I use at work.
Brilliant application, and nonesuch exists for WP.

The problem of the WP platform is not the UI which is after all just an UI. (I generally find all user interface stuff uninteresting and of relatively little relevance to anything.)

• The problem is that the platform is closed and you have to use is "as-is", you cannot DO anything to it or with it.
  The development tools if they even exist are alien and run on unfamiliar and largely unusable platforms.
• User data is not available on the device in any recognizable format, all is hidden away and the device is just a front-end for some proprietary cloud storage which makes it difficult and sometimes impossible to get it out of the device
• It is impossible to run any kind of development environment in the device, how are you supposed to extend it by yourself? There is no command line at all!