My understanding of the question ban (which is only pieced together from circumstantial evidence, like everyone else who isn't a SE employee) is that a deleted question is at best no different than an undeleted one, at worst only slightly worse.
The point is a bad question is a bad question whether deleted or not. Someone who constantly asks bad questions shouldn't be able to escape punishment simply by deleting the question. They need to be held accountable for the decisions they made to continue to ask bad questions and not learn from their poor choices.
But in general, the reason the the community considers deletions bad is because they consume resources. Not necessarily the physical resources of Stack Overflow (but they do consume those resources too) but the human resources of everyone who touched the question
- You are wasting the time of every user who read the question, whether they decided to participate or not.
- Anyone who commented or edit tried to help you. When you decide to delete, you basically eliminated their contributions. Yes, the comments might have been the reason you decided to delete, but that's beside the point. The fact that you deleted the questions means you felt that the question was unworthy of the site and it means that the time anyone spent on your question could have been spent helping another user.
- Anyone who answered (but did not get an upvote (yet)) or was in the process of answering basically wasted their time. You took the effort they expended on trying to help you and threw it in the garbage.
The point is act of asking questions should be considered a consumable resource. You aren't just posting a question on a magical site that automatically spits out answers, but on a site with actual humans on the other side who volunteer their time to help. You are actually consuming the resources (in terms of time) of every single person who encounters your question and when you delete the question, you are basically saying to those people "the time you spent looking at my question and possibly trying to help me was worthless".
We want you to think hard before you ask the question, not after. If you decide that it is a bad fit after you ask the question, you've already wasted people's time. So we want you to think about it before asking so you don't waste anyone's time or efforts, and those efforts can be spent looking at other questions.