Oofta
Legend
Nothing. I use the rules I like. So should everyone else. My preference is for Level Up's version over Matt Collville's though. Most of his work is too influenced by 4e's design philosophy for my taste.
I think one of the strengths of 5E is that they continue to support 3PP, even to the point starting to add content to DDB. So I don't see what the issue is.
No, WotC is no longer doing the book-a-month club. It never really worked anyway and led to confusion amongst casual buyers so they've decided to focus on their core books and modules. I think this is one of the things 5E did right. The books for additional rules expansions like this are still available for those that want it. No it's not "official". That just means that you can have multiple ideas on how to approach the same gap in the rule so, for example, you can use LU's version instead of MC's because it works best for you.
Meanwhile for those of us that don't want or need domain and stronghold rules but want different styles of monsters also have multiple options. All without confusing grandma about what book to buy little Sally because there are just too darn many D&D books published by WotC.