Probably a need for Solar power throughout the month. A lunar base would need a nuclear generator for 15 days a month or one heck of a battery system. Also probably easier to maintain a structure in microG.
A low earth orbit, like the current space station, has roughly half the sky blocked out by earth plus the magnetic field of earth to somewhat protect it. Getting to the lunar gateway's weird orbit, if you were already on the moon, could take several days versus less delta-v to just go to low earth orbit which can be done at any time.
Would be a better use of our research and money to build a power satellite and reflect or beam solar power to the base than to use LOP-G.