|There are a couple of reasons. To understand them you first have to understand the behavior of long pips, which it doesn't sound like you do. |
Long pips are said to reverse spin. This is partly a misnomer in that the ball actually continues spinning in the same direction through the impact with long pips. Then the spin is effectively reversed when it comes back to you, as though you hit into a mirror so to speak. But in truth, inverted reverses the spin. Long pips continue the spin.
On the lower levels this usually means people accidentally spin the ball sideways, or can't mentally keep up with what the ball is doing and they make mistakes and put the ball in the net or pop it up, allowing for an easy smash.
On the higher levels, the opponent isn't going to be tricked so easilly. The long pips are used for chopping because they can pass the spin through. This means that they don't have to chop though the ball as fast or faster than it's being topspun to keep it from popping up.
Also, very good long pips players can vary the amount of reversal by controlling how their pips bend when they strike the ball. Typically if the ball is chopped thinly it passes through most of the spin. If they dig into it it kills more of the spin. That variation is what makes it effective on higher levels.
However, on lower levels, your opponent may not be putting that much topspin on the ball. Therefore, they may not recieve as much backspin back as you would like. With inverted however, you can always chop a lot of spin onto the ball.
There are even choppers that combine some of both by using short pips. Some of the best ones in fact. But that's freakin hard to do unless you're awesome.
So in the end it depends on how you want to play. There are successful choppers using thin, tacky inverted rubbers and there are long pips choppers.
On the lower levels the glassy "frictionless" pips are effective. DrNeubauer is the primary example. He treats his with epoxy to make them glassy slick.
On the higher levels that doesn't allow the chopper enough ability to change spin to be effective. Most of them use spinnier long pips like feint long and tsp.