It's was not very high level of naivety to invest in ML back then, they did impressive marketing job and innovation most often happens in smaller companies - it is far more easy to acquire company shares than try to build a team - hard to hire experts, build labs and finally this requires time.
Note that ARKit/ARCore are steps required for this kind of tech - so at least Google and Apple are building expertise on AR/MR software technology, but the hardware part is still left for others to figure out.
Today except Microsoft there is Intel using Sony's waveguide simple display and other headsets that are not giving magic experience by using more primitive tech.
Anyway for me it is sad they still invest in ML only for this reason that supporting more players would greatly improve chances that some company would figure out better solutions and ML is stuck in local minima to keep most of their story and promises.
They sell dreams. Unfortunately they got social proof - "quickly, other already gave us a lot of money, you should too!".
There is already existing HoloLens tech which you can already buy.
Anyway for me it is sad they still invest in ML only for this reason that supporting more players would greatly improve chances that some company would figure out better solutions and ML is stuck in local minima to keep most of their story and promises.