Some try it since they see how some people go nutty over a toned coin. They see actual entire forums on toned coins. The Tonedcoin forum is an example so people think if they can tone a lot of coins, they can sell them and get rich.
Of course there are people that just want to have fun and attempting to tone a coin is a way of killing time and to them, it's fun.
In chem classes all the time coins are used as experimentations and if you can tone one, it's a chemical achivement to some.
And don't forget kids. They just want to try stuff they read on the ineternet.
And the reality is in some instances, an AT coin is impossible to tell from a NT one. All depends on who did what to what with what.
Someone I know sent in a coin to a TPGS that he toned himself and it came back in a slab, graded and no problems.