Unpredictable schedules is nothing to do with holiday work; that can be planned and agreed in advance, with suitable pay, and people will happily do it. What really grinds people's gears is "on demand / zero hours" scheduling: you have to ring up an hour before your shift starts to check whether it's actually going to start or been moved again.
With predictable scheduling you can work two part-time jobs. With zero-hour contracts, you can't (because they may whimsically decide to schedule conflicting shifts for you). And you can't budget because you have no idea how much you're going to be paid.
Retail and hospitality were infested with this nonsense, and as soon as workers have other options they quit it.
The hardest job I've ever had wasn't any of my software engineering jobs which paid six-figures: it was working at a retirement home as a dishwasher and food server. It paid $8.50 an hour (in 2007), and I didn't know my hours until the day before. It was hell, and I lasted two months before burning out.
With predictable scheduling you can work two part-time jobs. With zero-hour contracts, you can't (because they may whimsically decide to schedule conflicting shifts for you). And you can't budget because you have no idea how much you're going to be paid.
Retail and hospitality were infested with this nonsense, and as soon as workers have other options they quit it.