Why do LA's seem so underused?

I've played LA almost exclusively since launch (95%<) and only now feel I'm really getting the hang of it. A lot of times I almost gave up and turned to a class easier to grind certs with but as a TF2 scout/tribes player I couldn't get over moving so linearly. Now with 2 c4 bricks and a nova I've started dominating.
Any facility is a playground to a clever light assault, and there's no unit in the game (other than aircraft) that I don't hunt. Maxes, engis with turrets, tanks, snipers: provided I set up my approach well I can take out any unit I choose and often get away clean.

As an example, The other day, my squad moved into a lightly defended tech plant. I went over the shield to scout the defenses and the point was undefended, so I capped it. I held that point, solo, for several minutes taking out 12 TR, mostly HA or medics in the process just with clever use of JJ and my environment. I couldn't have done that with any other class.

my favourite class by far

You don't need skill so much as ADD. If you like to just hunker down and exchange pew pewies with the enemy, LA is not going to cut it. You need to keep moving.

Also I'm a little vary of using shotguns with LA since that will affect my effectiveness when it comes to roof snipin'. Then again I don't like to play around with loadouts much.

i love LA...got 2 C4 unlocked on...often i hide behind rocks when i know a tank is close by...when he gets close i charge over the rock fly over him drop drop...and press the button bOOOOOM cya sucker same can be done with infantry hiding in a group behind cover...just drop C4 as your over them lol...and enjoy the kill spree

I've been getting 230 Certs per hour with shotgun LA this weekend

To use LA effectively you need to think outside the box. A lot of times you can flank in surprising ways. Not a lot of people think outside the box apparently.