Why aren't there submission fees for submitting papers to conferences? Current scenario (A):  


Submit a paper for free. No matter the quality of the paper, submit anyway. What have you to lose?
If your work is accepted, pay to actually confirm the acceptance of your work, and present it to the world.


Proposed scenario (B):  


Submission fees: Anyone who wants to submit to a conference pays a certain amount. $200, say. Hefty enough to discourage 'spam' submissions.
If your work is accepted, you present without having to pay any extra registration fees.


I don't understand why (B) isn't obvious, from a quality control point of view, as well as a more obvious way of funding conferences. Only work that an author knows (thinks, really) is worthy of acceptance need submit, please.
There is already a strong incentive not to submit a paper that you know has very little chance of acceptance. While a paper is under review for one conference, it may not be submitted to another (according to the standard policies in fields where conference papers are "real" publications). If you submit a paper that is nowhere near ready, you hurt yourself: you block yourself from submitting a more complete version of it, that has a good chance of getting accepted somewhere else, for the entire review period.

Furthermore, many conferences end up rejecting lots of very good papers, due to limited space. What is the rationale for collecting fees from those authors? Authors would absolutely take their papers elsewhere, rather than risk paying hundreds of dollars to get a reasonably good paper rejected.

Finally: authors from less wealthy countries are already "priced out" of conferences to some degree (and have to publish mainly in journals), because of the cost of conference attendance (travel, registration fees). This would certainly make the disparity worse.