Many find the movement speed reasonable. Not to mention you have a horse, why are you on foot? Even the slowest horse trot is much faster than walking.
I mean I get that you're impatient and have places to be or whatever, but this is a legitimate design decision, which I imagine is tied to the focus on plausibility. Dudes sprinting everywhere might be cool in GTA, not so much here. If you don't like it, play something else, it's not like this is the only open world game on the market.
Hilarious condescension towards a legitimate criticism about the game. By your logic if everyone stopped playing because they didn't like one aspect of the design then everyone would have dropped it.