There is no way 55 million visas can be reviewed in any reasonable amount of time (cue the "AI can do it" comments). The number of H1B visa holders is a tiny fraction of 55m, if they cared about reviewing those, it'd require a lot less in time and resources.

Targeting H1b would also result in much stronger legal opposition. It takes a year to process less than 100k H1B applications annually, and companies have to pay thousands processing fees for each one. The goal of this is to discourage foreign students, refugee claimants and tourist visa holders from coming to America.