Indeed, I dont understand why either, can't they just fix what's broken and then polish it. Its also why I can't fully commit to WP, MS isn't fully committed to their mobile division(yet).
Microsoft just finished acquiring Nokia last spring (4/14) and have already released Microsoft-branded phones. Apple hasn't gone through any buyouts, neither have Samsung, HTC or LG. So let's look at recent buyouts and then tell me if Microsoft hasn't moved faster than others.
The last Motorola before the Google acquisition was the Droid Razr series in Q4 of 2011 (11/11). It wasn't until August of 2013 until the Moto X was released. Almost 2 full years between model releases.
The Palm Pre2 was released in October of 2010 and the HP Pre3 wasn't released (unofficially) until August of 2011. In fact, the phone was never officially released in the US due to the Apothecalypse. Almost a full year to release a phone that was basically a refresh of the existing line.
Even though it wasn't a buyout, during the transition from Research In Motion to BlackBerry, model releases were almost two years apart (Bold 9900 - 9/11 Z10 - 3/13).
Now consider that the Lumia 535 was released just 7 months after the closing of the Nokia deal and tell me Microsoft isn't committed to its mobile division.