There is legitimate use cases for a zero hour contract. The vast majority don't fit it.

If the zero hour contract minimum wage was £50 per hour, then it would be appropriate. This would still allow it to be useful to hire consultant, semi- retired experts and contractors and use PAYE, no additional companies, accountants etc. Very efficient and would only apply to employees with some power in the relationship with the business.

However, it's used to exploit minimum or low wage staff. The company takes all the flexibility it offers and uses it to bully the employee into accepting the hours the business wants. They do this by treating to cut hours if the employee doesn't agree. This makes it difficult to have multiple jobs to make up the hours.