Give them weapons that logistically fit their existing industry/supply-chains.
An M2 is NOT a special force equipment, nor a complex guided weapons (like Javelins/Stingers). Just like if you are supplying Afghans to fight against Soviets, wouldn't it be better to give them something that can fire 7.62x39 which they have an abundant existing ammo to resupply, instead of a 5.56 which once ran out of ammo, will be very difficult to resupply?
It's the same idea with the suggestions of supplying Mig29s and S-300 to Ukrainian, because it will be systems that their existing forces can operate, maintain, and use their existing weapons in storage.
NATO countries definitely have heavy machine guns that can fire Ukrainian rounds. Why give them a one-trick-pony M2, instead of anything that fires 12.7x108 like the DShK or the NSV. I am pretty sure former Warsaw Pack member nations has a lot of those.