You bring up an important, yet indirect, point.

The people would vote indeed vote for politicians who promised a bigger UBI. So these politicians should deliver on their campaign promises. This is how western democracy is supposed to work.

My ulterier motive on Medium is to promote an alternative democracy.

https://medium.com/discourse/tiered-democratic-governance-3f36a8f45660

I'm certain politicians under this new, TDG system would behave more responsibly with a UBI, ensuring the basic needs are met while still providing incentive to get a job. These TDG politicians would not be making campaigin promises (aka, bribes) to big demographics to get elected. Take a look at my link, and hopefully my book, which is available for a free read.