I think it may be because the game considers it a hostile action. Sort of like how attacking disables invisibility.

Imagine this scenario...
Fighter vs rouge.
Fighter can not see rogue at all cause his spot/listen is bad.
Rogue has 500 traps. The rogue can just stay hidden and just trap and trap and trap until the poor fighter dies. At least if he had to unstealth (Even if he had Hide in Plain Sight and was only visible for a second) the fighter at least stands a glimmer of hope in defeating him.