One problem is cost. It takes millions of dollars to do a truly scientific poll these days. Robocalls don't work anymore due to cell phone penetration. The phonebook is dead, and along with it any credible listings of numbers that represent real people. Plus very low response rates and spam filters blocking much of polling calls even then. You pretty much have to go door-to-door in order to get a truly good poll, which is something few organizations can do.

As a result, most cheaply done polls use non-random samples and add a giant "fudge factor" to make it look random. It's not clear how there models really work and there's no way to audit them.