Valve has money, but not Apple or Microsoft money. I doubt they'd be able to source a high-power arm chip + the necessary hard/software features to make something like the rosetta compatibility mode possible.
Not necessarily right now but a few years down the road when it actually releases(though no one knows when they'll actually release knowing valve's track record).
According to the article they are shooting for a late 2021 release date if nothing goes wrong. Fingers crossed they'll say more at E3, which they're attending this year.
Not sure why people are downvoting you either though.
Not sure why people are downvoting me....