Okay, well, even if the mechanic was on this creature:
Dude
B
Creature-Skeleton
Seclude 9
1/1
Why would the opponent ever give you extra 1/1's? One card out of the library is not worth giving the opponent card advantage. The cards with seclude would have to be incredibly weak, and even then the opponent would never choose to search with the seclude cost. It just doesn't make sense. Why give the opponent a free creature/spell so that you can lower the chances of them drawing a certain card (which are already not that high in a 60 card deck)?
Firstly because it allows you to get rid of pesky 1-ofs that may ruin your day. Also, it plays an interesting game of 'Can I deal with this now?' In the example of your card, it allows you to go, 'OK, if I get a Pyroclasm, I win.'
It also offers the ability to let your opponents outplay themselves, a not insignificant trait in a mechanic.