Neither am I, but it stands to reason that if there were only ONE US-flag vessel capable of doing a specific job and that job is reserved for US vessels, that would create a monopoly.
Besides, most oil companies require 3 competitive bids to award a contract.
The solution would then be to have more than one US vessel with the right capabilities, in which case there may not be enough work in the US market alone.
To build and equip a CSV to the latest and best standard at US yard exclusively for the US market may be technically possible, but is it economically feasible?
Alternatively; allow foreign built/US-flag vessels in US waters, but capable of competing internationally. Such vessels could be using US officers and foreign crews when outside US waters. (Better than no US crews at all)
If you look at today's reality, the large well equipped CSVs are mostly working, but moving between jobs around the world, incl. in GoM.
Even simpler MPSVs are better off than plain PSVs and AHTS, but it takes more than to put an AHC crane and a portable ROV spread on a basic PSV to make it internationally competitive.