What makes a novel a 'potboiler'?

The specific term 'potboiler' is said to come from producing works that are intended primarily to 'boil the pot,' that is, provide income to cover one's living expenses, by catering to popular demand rather than considerations of quality. A work might be said to be a potboiler if it relies on formula and cliched tropes rather than presenting original themes, or otherwise appeals to cheap sentiments while lacking emotional depth or artistic merit.

The term is used in a derogatory fashion, describing something written just to get some income, as opposed to being written with an attempt at literary merit.

A potboiler or pot-boiler is a novel, play, opera, film, or other creative work of dubious literary or artistic merit, whose main purpose was to pay for the creator's daily expenses-thus the imagery of "boil the pot", which means "to provide one's livelihood". Authors who create potboiler novels or screenplays are sometimes called hack writers or hacks. Novels deemed to be potboilers may also be called pulp fiction, and potboiler films may be called "popcorn movies."

https://en.wikipedia.org/wiki/Potboiler