UA does offer a no-fee change. It's called fully flexible, generally Y. Absolutely insane for UA to cannibalize it's HVC customer base to keep the deep discounters happier. They bought tickets with change fees. Waiving the fee is nutso, especially for someone with zero demonstrated loyalty.
For the same reason that UA (and other carriers) don't hand out freeloader UG's on international and will send an aircraft out with empty premium seats, they are preserving the brand.
Sure, once in a blue moon someone won't shell out the $75 and his scheduled flight is cancelled. But, that's infintesimal.