Yes. Yes. Yes. Please change this behaviour.
On the main site, deletion of negatively-scored posts by deleted users is all well and good: no point keeping crappy content around when the user themselves isn't on the site any more.
But on the meta site, it can cause problems. There, "negatively scored" isn't the same as "crappy"; and users such as spammers who get quickly deleted don't often acquire enough rep to post to meta. Someone might have posted an unpopular suggestion or feature request which, although declined, is still useful to link back to; this should still be available to the community if the user quits.
Note that answers as well as questions fall prey to the auto-deletion scourge.
A recent example has caused a certain amount of havoc on Science Fiction & Fantasy. A user went from being a very active and valuable meta contributor years ago to rage-quitting and deleting his account last month over accusations of mod abuse. He'd posted several answers to a very important meta discussion on the site's scope in 2011, and three of these had been heavily downvoted, reflecting the fact that those types of question were decided to be off-topic. I only recently discovered that these answers had been auto-deleted, and had to undelete all three of them so that we still had a clear record of decisions on the site's scope - a pretty important thing to have, you must agree.
There could be many other useful negatively-scored posts by this user which have been auto-deleted and which I haven't yet found in order to undelete them. This is not a good state of affairs.
(more-or-less copied from my duplicate question here)