They all back slap, hand job each other on their final poll the night before the election and the attention span of the general populous doesn't see that they all tried for the longest time to sway the vote with by using "general population," "registered voters," and/or "likely voters" to skew their results.
Even RCP likes to aggregate likely and registered voter polls. Also, the sample sizes are way too small. Micro-polling is where the real info comes that the campaigns use.
Simply put, a “registered voters” poll is completely worthless. It doesn’t matter whom is doing the polling. If you’re not actually voting, your opinion in a poll on a given political race has zero bearing on the outcome.