Because sony smartphones and tablets suffer lot bugs and are outdated when they hit the market, not to mention because sony is slowest when it comes to releasing updates.
Also their lot bugs like random shutdowns or laggy ui etc, lets also not forget that android 4.3 and 5.0 might be comming out soon, and sony still updating their smartphones and tablets to jelly bean 4.1.2 not even 4.2.2.......