It really isn't that hard to run an online poll. A select number of websites such as AFI could do all the work for them. Hasbro has utilized websites to poll fan choice figures in the Star Wars line before, so why can't Mattel do the same with its DC line?
For 'limited resources' look under 'can't be bothered' in the phrase dictionary. Basically it would require them being a bit proactive in getting such a thing set up. It wouldn't cost much if anything, but it would require a tiny bit of effort and willing. Plus it's not their idea so it'll get shot down straight away.
I still believe if they looked at their tooling budget for CIE, and drew up a list of possible characters that are viable for them to make, offered those out to fans to choose from, then made the winner, it would help generate interest and sales in the sub.
Take the upcoming Red Hood figure, if they had shown that version, the Biker jacket version and the classic Tux Joker version and asked us to vote which one we wanted, the one we're getting would've never stood a chance.