Catch22. By looking after them you maintain or promote a unionised workforce which ultimately will benefit all crews going forward. Ignore them and you marginalise your existing crews in the long run. That's before you begin to address the other significant issues about zero hour contracts such as FO's reporting unfit for duty, the emotional baggage they often inadvertently bring to the flight deck and the subsequent stress it places on captains.
Yes there are plenty out there in an even worse position but you have to deal with the issues on your own doorstep first.