It's not a lot of it and isolating it is more trouble than it's worth. It's easier to just create a lithium channel that creates it when it's neutron activated. That or isolating it from a heavy water reactor, since that produces a whole lot more.

Tritium isn't scarce, in that we really can create it pretty easily. Lithium-6 is available to do so if needed. (https://isotope.com/en-us/lithium-6-metal-li-95-pct-llm--827--pk). It's jut not economical to produce for most purposes.

Edit: Also, it's not tritium in the regolith but He3, which is theorized as an aneutronic (thus much cleaner and not creating a bunch of neutron activation waste like tritium fusion would create) fusion fuel but nobody's really achieved fusion with it. Tritium would've decayed if it was in the regolith.

When you let tritium decay, it creates He3.