There's a lot to be said for 26" wheels. I like how easier it is to store my 26" bikes, or take it on the trains here where the bike compartment isn't big enough for a 29er. I also like to be different (or eccentric or mental) when I do MTB marathons on 26" wheels, since almost everyone now believes 29ers and 650b are so much faster than 26" (not true). Yes, depending on the terrain a larger wheel can be slightly faster, but it's barely significant and at the few per cent level, not the tens of percent that seems to be implied by some of the marketing. For riders who are really worried about being a few percent faster, there are several cheap ways to become faster (tyre choice, tubeless, barends etc.).
At low-ish price levels, you can build a better (and faster) 26" MTB for the same money, compared to a 29er or 650b.