The main problem with the mentor system is they still have not made any obvious way for new players to access it. They barely even mention that it exits, if at all. I've played on sprouts a couple of times lately, and even on Balmung, I haven't received an invite without asking.
As far as being the old vet going through FFXIV Gil the leveling dungeon motions, I do not like to rob the new players of the chance to actually be new, and for the most part the content in question is simply never a problem. I even don't bring up the bomb thing for the slime fight in copperbell unless someone actually kills them (please learn the hard way like I did in 2013!)
XIV IMO impresses you the most when you're new. The scope of the game simply seems huge when you haven't played for years. I simply don't like to interfere. I don't inform new friends on the game of much of anything either unless they ask.
Having made a few alts myself recently I've had about the same experience. I think part of it may be due to everyone having quit playing after beating all the content. Either that or they just quit like a bunch of my friends since the recent story was kind of lackluster and they got bored since every patch is the same tome grind.
I've had the exact opposite experience. Too many people trying to explain the fights to me when the New Player message pops up, so much so that I've created a macro on my alts that says "I know I have the Sprout, but this is an alt character for me so I already know the dungeon".
I think they made that sprout stay around way too long now.
It stays on till I think you finish ARR storyline or 140 hours.
So seeing the sprout doesn't tell me anything. Could be your second run could be your 20th run. Could be your alt. All of which I don't think you want me explaining a fight you know already.
I have never seen, anyone ask for Final Fantasy XIV Gil help and not have me or someone in the party explain it. Even if a very basic "dodge stuff" since many boss come down to just that.
So I don't think its so much a lack of players. Its just the fact that most of the player base has done the content for 2+ years and if you need help speak up but acting like every run is a new run isn't necessary.