Do you not purchase insurance? Same principle. Collective bargaining and buying power unlocks things even you, a wealthy above average human, might wish to have affordable.
> Why should I as a non-unionized worker today join one?
So they continue to exist and rules don't slide back further.
I mean if you are old and rich enough enough not to care about the next decade of working life then good for you, I guess. But society could very well be ripped apart by the very things that the tech industry is rolling out, and unions are one of the few things that stand in the way of absolutely massive regressions in the way humans who have the temerity to want to eat will have to tolerate being treated.
Personally I want to see them survive, and non-union workers joining them when they can is one of those ways that can happen.
(As an IT freelancer I cannot, meaningfully; I assure you that when my work pattern changes I will)
If that's the best case you can make, they're even more useless to skilled workers than I thought.
Would you like to buy some insurance against aliens destroying the earth as well?
Fearmongering and/or hand wringing about what could get worse in the future doesn't change that reality today.
The big risk to a worker is that they overestimate their skill level, which absolutely does happen, but those people are not in the above average pool I'm talking about in the first place and would in fact benefit from a union.
All above average employees I know don't need to worry about staying on the better of average for some arbitrary metric. If the company makes a mistake and fires them, they can quickly get a job elsewhere. It's the people who have no better alternative than their current job who need the protection provided by a union contract, and they have no better alternative because the company made a mistake in the other direction when agreeing to employ them, and the union's job is to bar the employer from correcting that mistake.
And yes, unions successfully fought for improved work conditions 100+ years ago. What have they done to earn their keep during the careers of anyone posting on this site? Why should I as a non-unionized worker today join one? It's certainly not going to improve my total compensation, and the people who did the hard work you mentioned are long gone so it's no benefit to them for me to pay dues into an organization they were affiliated with at some point.