The short version is that established accounts with a post history have to request deletion, because it can otherwise severely impact a community.
If you were the OP to a long standing topic, and your deletion annihilated the entire topic that would be problematic. Community managers need to assess the impact and take any necessary precautions prior to deletion.
Communities aren’t like email accounts or file sharing services, you have the right to request your account and any PII be removed, but that right doesn’t override those of other users.