It does affect the RPG element to it. In BC, the high cost was the riding skill, but to get a unique mount took effort and/or luck (e.g. the Amani War Bear mount). Now, a unique mount is for sale for real world money and absolutely no in-game cost (which was a consideration back then). That's not what many people are looking for in a classic experience.
Sure CE stuff was available back then (I have them all), but they were pets that most people don't even notice (I still pull out my panda cub and *very* few people comment on it). It's a big disingenuous to compare a pet with a mount in the classic expansions.
Is it a huge deal? Not really. Is it nothing at all? Also no. Don't straw man the issue.