Exactly, however, newer players should realize that Gliscor can pass the same boosts, has access to Taunt, and is much sturdier.The answer is relatively simple as to why Ninjask still sees use. Quite a few players (especially newer players) see Ninjask as the easiest way of passing stat boosts to Pokemon. I mean, think about it. It's easy to get a +2 attack +3 speed (or similar) to something deadly like Tyranitar, Salamence, Gyarados, or anything else that can deal massive amounts of physical damage.
The reason why I say newer players use Ninjask more is because, in paper, Ninjask seems decent. However, Ninjask telegraphs your moves to your opponents. Nearly every Jask is a passer (hyperbole fail). It takes almost zero effort to use Protect, Sub, Swords Dance, Baton Pass, pretty much in that order.
This makes Ninjask extremely easy to counter. Even a +2 X-Scissor fails to pose an adequate threat to a defensive minded Pokemon. Its ability to be pseudo-hazed means that its passes are usually for naught. Even if Ninjask comes in on something other than a Pseudo-hazer, all one has to do is switch to the hazer and spam Roar/Whirlwind, blowing away the stat boosts the moment they're passed. In addition, Stealth Rocks take 50 percent from this bug, and factoring in subs, Ninjask usually gets only one chance to pass, and that one chance is easily denied.
But again, some users fail to realize how easy it is to counter Ninjask. If you don't stop Ninjask, there's a chance you'll end up 6-0'd. It works both ways. The inexperienced user doesn't know what to do against Ninjask and gets swept. The inexperienced user of Ninjask thinks that Ninjask is a good lead, leading to its higher usage.
And Aerodactyl gets screwed by Bullet Punch Metagross.
Luckily, Ninjask typically passes to something it shares a weakness to, so if you can predict which recipient they are passing to, you can hit them SE. Salamence, Gyarados, and Ninjask are weak to rock. Tyranitar and Ninjask are destroyed by Bullet Punch. Metagross is weak to fire. Marowak is weak to ice. Unfortunately, if you mispredict and use a rock move, the latter two could come in and rape you. Still, just pressing the point that most teams can beat Jask passes without a pseudo-hazer.