Industries with high levels of unionization tend to have lower turnover, which can be good for employees already inside, but can make it harder for new employees to join. They also can have various rules, like seniority, that take precedence over other forms of promotions (whether meritocratic or not). Unions are also inherently political where membership voting, with all the internal dealing, agreements, possible corruption, drama, etc that entails causing issues.

Not all unions are the same. There are absolutely unions that are as bad as the naysayers say, but there are also ones that you rarely hear about that just quietly chug along with decent enough relationships with employers.

That being said, the appeal to me is minimal. I like working for small to medium sized companies where I can enjoy the flexibility of what tech stacks I work on. While the idea of some sort of optional trade union that could cover me for benefits, legal fights, contract enforcement, and maybe extra job insurance is appealing, nothing like that exists where I live. I have gotten healthy severances in the past due to knowing the rights I have in my jurisdiction, but that also means having the will and ability to hire a lawyer.

I'm in my mid 40s and rode the wave of a workers market over the last 2 decades. I'm still in demand, too. It's not quite as easy as it was 5+ years ago, but AI hasn't replaced me, though I'm actually "supervising" its work from an experienced angle. From that perspective I'm just a lot more productive.