when people are on 0 hour contracts, the company still has to pay social insurance for the employee. Some of which are not bound to the hours worked.

Also, a 0 hour contract is a iffy construct. If someone can show they worked N hours on the regular, they have the right to get a contract on the amount of hours they worked. Also, 0 hour contracts are only allowed for a limited number of times afaik. (2x up to one year i believe).