There’s not plenty of helium-3 in lunar regolith (which is simply the floor layer, and is the one layer that accommodates any in any respect) – it is within the tens of components per billion at greatest. Meaning amassing and processing billions of tons of regolith for a number of measly tons of helium-3.
Which is not all that helpful exterior some area of interest excessive cryogenic functions. It isn’t a worthwhile fusion gas – it produces much less vitality per fusion occasion than normal D-T fusion, and can be fairly tough to ignite and maintain (we do not but know the Lawson Criterion (issue to ignite) for 3He-3He, however we do comprehend it for D-3He and it is 16 instances tougher to ignite than D-T). The only “benefit” is that 3He-3He’s aneutronic, however the neutronic emission from D-T is definitely helpful for breeding extra gas.
(Oh, and if we needed to, we will manufacture helium-3 proper right here on Earth. It is what tritium decays into.)