I'll give my two cents here.
Ignoring the bloggers and other media sites lets look at those who are a bit frustrated, those who have been with WP for some time and have done the 'waiting'.
If you look back to October 2012, the introduction of WP8, yeah a little less than four years ago, a lot has changed in MS but little has changed for WP other than the loss of market share and the continual lack of confidence from the consumers or users if you prefer.
There is nothing wrong with W10M on the whole and nothing wrong with the ideas that MS is trying to achieve. There's nothing wrong with them dropping consumer hardware and leaving OEMs to pick up the slack. All good business decision. However, business decisions don't get you users.
I will put it this way, W10M currently does not perform well in what people want in the current market of smartphones, which is in the apps arena. I'm not saying this won't change but that is where we are now. That's why W10M suffers and will continue to suffer while this remains the status quo.
It hasn't helped that it's been continuously shunned by developers. People are going to take a dig at it. Users will get fed up. People won't bother. Regardless how good that OS may be.
It doesn't help that MS has made so many shifts and changes in the last four years either. If you look back over everything it feels and looks like a giant mess of ideas and dead ends. It's not a pretty sight.
I know there is no such thing as the perfect OS. There's no such thing as perfect hardware either. No provider is without it's issues. However seeing the slow implementation of W10M is rather painful. A lot of people wonder if it's worth the pain of the constant updates to stick around. I'm not personally into Stockholm Syndrome myself...
I think MS has a good idea and is doing their best to implement it. They have a very long way to go, which for those who want to do things now are tired of waiting for. I think regular consumers are just getting tired being told to wait more.
The frustrations you see on here is based on those who feel MS has failed them. By not providing official updates for their devices or having updates make a mess of their devices. It's only natural to get upset by these two things. Add in the lack of apps and a feeling that no one really cares about W10M, whether perceived or real, and you can understand why you see the comments you get. Especially if you're a long time user.
As for the bloogers, I'll agree with the others and say it's purely based on money. Then again, what does W10M offer those who believe apps are it?