Because the pump is a RPITA. Say what you will, pumping up a road bike tire to 100 psi or so with a pump the size of a big cigar just ain't no fun. You bother with C02 (wait, what do you mean bother?) because it works great and is fast, cheap and easy. Tough combination to beat. Or you can beat your head on the pavement. Your choice. Oh, I forgot that Lezyne pumps are made by magic elves under a tree in the forest. They are WONNNDERFUL. Oh please, give me a break.