They do save.
Its not in salary that you see the money. The savings are in training and legal costs.
The average tenure of an HB1 is much longer than a US citizen. Turnover is lower for obvious reasons.
Threats of litigation , etc are much lower too. I havent seen a single HB1 sue their employer. Similarly, i have seen multiple US citizens sue employers, and almost always without merit (often it was to stave off termination, retaliate, etc).
There is alson some risk in a US worker. There is a lot of entitlement even at the high end. I have seen many native engineers and even PMs hit bars every other afternoon...on a 3pm weekday.
These were people close to 200k year.
The HB1 is a shield against that risk (or poor hiring), and thats savings too