100K in Bay area is not equal to 100K in some other part of US. Also H1B is not only used by the IT industry but other industries as well, where paying 100K may be tough.
There are alternate rationales where it would be justifiable to support an H1B-type system in that case too, but the H1B system's stated rationale isn't to allow companies in lower-cost areas to hire cheap-ish labor when they aren't willing to pay the national going rate for the talent they're looking for.