Looking at unions from a personal lense can make them seem unnecessary and maybe even negative to some people. However their purpose in my opinion is to benefit the collective of members as a whole.
I have nothing to back up this claim, but it seems like selfishness is what caused reduction of unions in the US. And for the same selfishness it's tough to organize people and kickstart a new union.
You have to show they actually benefit the members as a whole. Union laws in the US are extremely strong, and anti union sentiment is largely a hangover from the 70s, where features of unions limited our manufacturing sectors ability to compete internationally with catastrophic consequences for the Rust Belt.
I have nothing to back up this claim, but it seems like selfishness is what caused reduction of unions in the US. And for the same selfishness it's tough to organize people and kickstart a new union.