All Hell Breaks Loose - S3-E22
Question: Later in Charmed they bring the so called "cleaners" in episode 6-2 when Wyatt conjures a dragon and magic is exposed. Why didn't the cleaners appear earlier in this episode when Piper and Prue exposed magic?
Answer: Because they wanted them to fix their own mistakes.
Answer: That was a mistake in the series.
Also, the episode is called 'Babies First Demon' and this alone tells us that it's Wyatt's first time in the field (so to speak) and as the sisters say, they've done a good job of clearing up their own magical messes so far. Nobody really knows how advanced Wyatt's powers are, or will become. That's why the cleaners appear, to nip things in the bud. The Cleaners didn't want to chance that the sisters could clean Wyatt's magic up, just incase they couldn't. Therefore intervening themselves, just in case.