@runoutgroover @joncounts @ClareBear my pet theory is that for lots of reasons, parties nowadays prefer to campaign around turning out existing voters from their base and focusing on the small pool who change their minds. No one wants to cater to that 1.9m because they are hard to turn out, and doing so reduces the resources available for the easier pool of people who actually do vote. Consequence, why would you vote as one of that 1.9m? No one is offering anything you want.
There's also the fact that people don't vote if they don't think their vote makes a difference, and if your perception of what's on offer is that your life won't change no matter which of them wins, then why vote?