‘Ask for more’ is different from ‘Get more’. The labor contract is a negotiation. Ultimately, the only card unions have to play at an impasse is a strike. If they use that tactict the workers of the union won’t get paid while the contract is unresolved.
Let’s say you’re supporting your kid, don’t have savings, and are offered a raise and some meager time off. Do you feel like you have the freedom to push harder, ie go on unpaid strike longer, or do you vote to accept the deal and get that paycheck again?
This is absolutely true for a lot of people. A salary isn’t guaranteed just because you’re in a union, and it is often a lesser salary on strike to preserve funds. I think this person was asking about starting a union too, so there would be no fund set up unless they joined into a larger union.