It makes no sense to give something away for free if even a few people are willing to pay for it. They know that some people will be willing to pay the change fee, and they aren't going to forego that revenue. Airlines realized long ago that there is no value in creating happy customers.

Sometimes you can convince the airline to rebook you on the earlier flight at no charge, but you have to frame it in a way that makes it seem beneficial to the airline. For example,

"I have a tight connection and if I miss it the staff at ORD will have to re-route me and there may not be many options, so it would be better if I take this earlier flight"

"There may be fog at SFO and my late flight might get cancelled, so if there is room on the earlier flight, I should take that instead to make it easier."

Mention IRROPS, or the potential for IRROPS, and you may have better luck. Don't make it about yourself. Also don't bother the GAs when they are busy, wait until boarding is complete and the doors are about to close.