Here they are, briefly:
1. Until Citizens United is overturned by a "corporations aren't people" constitutional amendment, conservatives will purchase the votes of the 10-15% of voters who are both low-information and easily persuaded by advertising.
2. Citizens United isn't going to be overturned for a long, long time because state legislatures will be Republican for a long, long time. See #1, above.
3. The effects of conservative government will have to sink in -- from the end of Medicare as we know it to the end of just about everything else as we know it -- before that 10-15% block wakes up.
4. Demographics are a long-term plus, but only long-term. In the short run, voter suppression plus vast conservative ad campaigns can't be overcome.