Not voting means the party has to start offering policies to entice you back.
That's an assumption. Another assumption is that they try to win over the voters who reliable show up and ignore the ones who don't as unreachable.
How do you ensure the outcome you're looking for happens? Hope is not a strategy.
Vote for the furthest left-wing candidate in the primary.
Vote the for furthest left-wong candidate in the general.
It's not difficult.