It really depends on what you want from that deletion.
I agree there should be a way to remove the evidence of your involvement from the community, should you wish (often called the right to be forgotten), and that does exist. Should you wish, we can anonymize your account, which removes your profile, replaces your username with a randomly-generated one, and so on. No trace is left of you as a user of the forum.
However, the discussions you have participated in are part of the history of the community. Topics like Cannot deprecate a collection plugin would make no sense if your messages were removed but others were left behind. We’re happy to go back and redact where private information might have actually been shared, but removal of all messages would materially impact the community.
If you do want to anonymise your account, let us know and we can do that for you - we’ll be sad to see you go, but your have the right to do so.