Asisreo
Patron Badass
I think they do care, just a little.This only matters if you go through with the idea that, on the face of it, your actions will directly impact your advancement (outside the gear-acquisition component in genres and settings where that's relevant). Frankly, a lot of players don't really give a crap about that, or original RQ style advancement would be more popular than it is.
Have you ever had those scenarios where you have a fairly high-level adventure set up. The DM had a cool sequence for traveling. It isn't about draining resources, but its about exploring the world and enjoying the immersive worldbuilding. Stuff like climbing Mt. Doom or walking through the Valley of the Damned.
You ask the players if they're ready to set off and the wizard says "Can I just teleport there?" No matter what, its kinda a dissapointing feeling, right? Even if you say "No, magic is preventing your from teleporting," it shows they didn't really prioritize the journey. Why? Most likely because they've never been given incentive to explore the world like that before. Exploration had been nothing but meaningless worldbuilding that's irrelevant to their current quest.
XP can be a way for them to engage in the world. Trekking through a dangerous land can now be seen as beneficial, almost like training to before finally getting to the boss. They may even catch a level or two on the way, which is incentive.
I'm not saying XP is the cure-all for disengagement, but its at least a factor that could prove useful for a DM to incentivize immersive gameplay without railroading them down the specific path.