I agree it is a nice touch. That being said - when I have hired over the past 10 years I have scheduled round robin interviews with multiple candidates during the same day. (especially if I had more than one position).
The candidates move through a set of interviews cross functionally and in my function on top of seeing me.
At the end of the day I sit everyone down and we rack and stack. Usually 1-2 are must hires. Several are tossed immediately. Then it is down to the debate on the middle ground which usually came down to my gut on group chemistry. Within 24 hours HR is told who to make offers to.
A thank you note wouldn’t arrive in time. In fact a few sent thank you emails but the decision had already been made.
The Lion’s share of employers don’t hire that quickly, which is why this technique works.