It's one thing to say that in tech people can have different performance levels. But stuff like PTO, actually meaningful sick leave, maternity/paternity leave, retirement benefits, healthcare, workplace safety, overtime work, using people for work they have not been hired, equipped or training for - there everyone is in the same boat, but tech's aversity to unions has an effect like the infamous "crabs in a bucket" mentality.
Even wages... it's not "just" performance levels that dictate these. Unions also serve for those who are not as conflict-happy or those who cannot negotiate due to external factors (e.g. visa enslavement, they have family to take care of and can't afford the potential of being out of work for a couple weeks while they set up new employment)... unions sacrifice a bit of individual wealth for common wealth for everyone.
Informal organization (i.e. without the legal protections that formal unions have) only works in industries where the staff isn't fungible. A warehouse, fastfood chain or a lot of IT industry has the advantage for the employer that the staff is fungible. Fire everyone, pay a bit in fines for anti-union activities, and hire fresh staff that won't unionize because they know what happened to the last ones.