Snark aside, Sprint had its TP cost removed for the sake of the Feast, where it otherwise would have given casters an unfair advantage (considering they don't use TP at all). If they can remove it for PvP, there's little reason to keep it in PvE content. And again, with both game modes in mind, instant mount summoning would be beneficial, and a nice QoL change in general. Maybe it'll help people get to hunts or unspoiled/ephemeral nodes a little faster? As it stands, unless there's literally a technical reason why, there's no reason why not to have instant mount summons.