There is a mechanism to prevent this, any answer with a positive score prevents deletion. There are also valid reasons to remove your own question, the most com

There is a mechanism to prevent this, any answer with a positive score prevents deletion. There are also valid reasons to remove your own question, the most common is that you discovered a mistake that makes the entire question irrelevant. In that case you don't want a bad answer stopping the cleanup. Deleting good content without a reason is against the rules, it just isn't enforced by technical means in all cases. This is where moderators come into it to handle those cases, but you have to know to flag them for this.