This game has big enough of a problem with everything you do feeling pointless.
You get new gear? Cool, but in 3 months when a new "Season" starts your gear is all useless and catch up mechanics will give better gear. This feels HORRIBLE and is, in MY opinion, the worst part about current WoW.
This is the reason people enjoy farming Mounts and Transmog. It feels like an investment. You know that in 3 years you will still have said Mounts and Transmogs.
This is also why so many enjoyed the Mage Tower in Legion. It let you unlock some great Transmogs but also denyed us from just waiting for BfA to get the unlocks ez mode.
The same can currently be said about the Path Finder and Allied Race unlocks. You unlock it and it feels like an investment.
If they just let people get the Path Finder and Allied Races from the previous races the moment a new expansion releases, it completely ruins the sense of investment feeling it gives. Then, suddenly, everyone will question why they bothered spending all that time unlocking flying mount when they could just wait for the next expansion. It will go from feeling like an investment to feeling like a huge waste of time.