It all depends on country and at the stage of their development and industry you are in TBH. Some federal laws in some countries offer great protection to employees so unions are not needed to challenge if you loose your job on unfair dismissal.
100 years ago unions made sense.
For blue collar workers it makes send to have unions who offer strong support as generally they all do the same roll and can be measured against similar rolls around the country/world.
White collar office workers not so much as everyone pretty much has an individual role so hard to argue if you getting a fair pay or not when every job is unique. When it comes to negotiate wage increases generally a employee collective group do that. It goes a little like this, company offer 2%, employees counter with 3% increase, they always land in the middle lol.
Some unions are a toothless tiger. Will convince you that you are within your right then they backdown when things get difficult and the employees suffer.