A lot of players love getting xp. I suggested using milestones in my regular group a while back (wanted to try it out) and the player's vehemently objected.
We're using milestones in the other group I'm playing in, and while it is tolerable, I have to say I miss xp. There have been times where I called a delve short because we had accomplished our goal, despite that there were more areas to explore. The DM was surprised. I explained to him that while there might be treasure in those areas, there would almost certainly be danger, so the risk/reward ratio wasn't worth it. When we're forced into an encounter in that game that yields little to no treasure, it feels like a waste of time, unlike with the other group where we get xp so we feel like it was worthwhile. Milestones certainly have their upside as well, but they aren't for everyone. I still prefer using xp.