Why didn't or doesn't Ash catch Jigglypuff?

Her Sing is very powerful to put nearly all Pokemon to sleep. Ash could use the sleep advantage to get easy attacks and kills.

@thorson: wigglytuff is a beast.

Kills ?

@kgb725: Sssssshhhhhh....

It's been awhile, but doesn't anime Jiggly put everyone, including Ash, to sleep? Too risky.

Cause hes a dumb ten year old.

Fat and ugly.

Because Jigglypuff jiggles and puffs.