Unionization improves conditions everywhere over time. When a significant proportion of jobs are unionized even non union jobs now need to compete with the union jobs. Unions set the standard.
You’re right though that one store at a time won’t work. It needs to be the entire company at once, otherwise as you say, they’ll just close that store.
Changing your standards is a nice idea, but it’s not always practical for people in less privileged financial positions. Capitalists learned to keep their workers living standard bad enough so they can’t save up to improve their position but not so bad that they get completely desperate and revolt.
The 40 hour working week and 8 hour work day were originally fought for by Australian unions and are now a widespread standard for full time emoyment. Americans in many ways don’t have a clue what strong worker rights and regulations look like, and I encourage them to see what they could have if they fought for it.
It’s exactly the people in less privileged positions whose standards matter the most. I live week to week, I’ve been homeless, I’m not remotely well-off, but the job market right now needs labor enough that my standards and decisions matter. And there’s enough roughly equivalent available employment to make that happen.
Personally, I got a new job on the first of the year and quit on the spot.
I take it you’re solo and able to make those sacrifices but others may have family to support or not be in good enough health to be homeless, or be in a marginalized group where being homeless is flat out dangerous. Were you on the streets or did you have a car or friends and family to crash at? I agree it’s important to respect your standards and not let companies take advantage of you, but some people cannot go without a job due to responsibility, health, or safety and in those cases unionization is an important tool to be able to exercise your power as a worker without having to deal with quitting.