Didn't this start when they prematurely shut off support for older versions of IE? The users got a choice of going to IE11 for supported operating systems.
Then, they introduced a second browser and so they lost even more to mainly Chrome apart from last month when there was a substantial rise for FireFox...
Personally it does not matter as IE has been blocked from accessing the net since Windows XP (and now even Edge) and so they both work as my offline browsers only.
Still in my opinion, it seems Microsoft have been doing a lot of bad decisions lately. The next bad move is their new UWP Explorer found in the insider-program, from what I can tell, a move to get more people to adopt what first started as Metro apps, later Universal apps and now Universal Windows Apps. A new entry-point and a little gimmick can't hide their deeper wishes for a glorious Windows store which is seemingly their entire point :Z