It's sad that hunting horn is the least used weapon, at least according to the first wyverian on PC... and apparently lance is the second least used. I imagine people don't like lance because the main attacks aren't very flashy compared to the other weapons? Hunting horn on the other hand is just really hard to play well with, plus there's the learning songs etc. to contend with that isn't very helpful for a beginner dooter. Plus, people consider it a 'support weapon' even though it can do some pretty good damage as well as KO.
As for myself, I like weapons with shields. I should try playing around with Charge Blade more, but Lance is my crutch and it's hard to play without my crutch.
I feel like I'm running into the cool people who play the cool underused weapons recently, wow! Lance is one of my other favorite weapons in World along with Hunting Horn (closely followed by Switch Axe and a bit of Sword and Shield). And yeah, it is super unpopular, partially because it's boring, like you said, and partially because its damage tends to fall off, at least compared to a lot of the other options; the lack of a dedicated high DPS burst option on downed monsters doesn't do it any favors.
The obvious upshot is, a competent Lance user will easily deal 2x the damage of a less competent
anything else user over the course of a hunt, because the weapon is so consistent and safe.
I'm really looking forward to seeing what Monster Hunter Rise (the upcoming Switch title) will do for these two unpopular weapons in particular. With the addition of wirebugs, it looks like every weapon will have a decent fast approach option, which could benefit Lance a lot. And we've seen
zero footage of Hunting Horn in Rise, so they could be doing just about anything with it. World did a lot to make the weapon more comfortable to use... I really hope Rise gives it some additional spice.
Edit - As a side rant, I kind of understand Hunting Horn's lack of popularity, but Lance being so seldom used just bugs me. What could possibly be more badass than holding up a shield and standing your ground to tank a gigantic fireball/bodyslam/explosion/laser to the face while the rest of your teammates cower in fear and roll in every direction to get away?! No other weapon makes me feel invincible the way Lance does. It's
glorious.