Of course they are unable to fill positions at a given salary level. It's quite hard to find tomato-pickers at slave-like wages.
I had a H-1B visa once upon a time, but I never moved to the US. The company wanted me to, but I preferred London to Santa Cruz. Didn't stop me working for the company remotely, paid out of their UK sales office. Now I don't know what proportion of H-1Bs are like that - a global search to fill a local position - but it's definitely non-zero.
(The reason I'm pushing back on this is because I don't want HN to be a happy home for the same sad sack of devs Slashdot hosted when I last frequented there some years ago; "dey took our jerbs" was a constant refrain any time H-1B came up.)
But the first five times being told that the company has no matches for me.
Meanwhile, the company complains it can't find engineers.
How do you know what skills Microsoft needs and why do you assume they pay slave wages?