or it could be to fill the funding gap
assets.publishing.service.gov.uk/media/69260d...

Only some % of responses will be those switching parties. A good proportion will be from party x to Don't Know/Won't Say.
Analysis by pollsters shows a not insignificant part Reform's vote come from previous non-voters.
Sankey diagrams help explain what's going on.

Labour Party Clause 1: Object[ive]s
It's purpose is to organise and maintain in Parliament and in the country a political Labour Party.
The Party shall…promote the election of Labour Party representatives at all levels of the democratic process.