Answer 1

Not available on website

Answer 2

Camillo Porrati

Because mobile users are more than computer users (more than 90%) so they developed for only mobile users and also mobile phone can be carry and use anywhere.

Also you need to write few lines of code on Sololearn so I don't think it is annoying.

And also if Sololearn provide a terminal to write and run code so I don't think you need to write code on computer then copy here. If you will get any error then you will go to write code on computer? It may take more time than usual.