Earlier quoted context omitted.
I can already negotiate better than my coworkers. Why should I tie my compensation to theirs?
Because if you and your co-workers all negotiate together, you have more bargaining power and can extract much greater concessions.
Unions really fight against performance based differences...
https://www.nytimes.com/2019/02/11/us/denver-teacher-strike....
https://www.huffingtonpost.ca/michel-kellygagnon/union-perfo...
As it turns out, union contracts don't just set minimum prices that employees can be paid; they also tend to set pay ceilings that employers cannot exceed without the union's permission--and that permission is rarely forthcoming. Paying the most talented, hardest-working employees more than the average Joe who barely works to rule is not allowed, you see.