TLDR:
They are doing the same job, why would they not get the same pay?
Target has a pay by position structure with merit based increases. The pay range is tied to the position, not the person. That means if you want to earn more, then you have to do more. Better performance = more pay. Performance/merit based pay structures are great, until you come into a period of time where inflation outpaces wages and you end up where you are now, which is at square one.
Most of the world works on position/merit based pay so if you want to earn more based on time in position you had better find yourself a union job.
Unions in general are a powerful thing, but in retail, specifically in big box retail, there's zero chance it ever happens. Someone may feed you some bullshit feel-good story about how you can organize and work together but corporations hold the cards. They have billions of dollars, thousands of locations, and nigh infinite overhead. Unless by some miracle every employee ever unionized at once,
they'd simply close the store and be done with it.