Earlier quoted context omitted.
Why do you think unions would mean salary cuts? Unions don't set maximum salaries. You are absolutely free to negotiate your salary, raises, promotions, and so on. In the Nordics quite many tech workers are in unions. For most people it's perhaps just about habits and solidarity, but they do offer tangible benefits like free consultation and legal representation in a case of dispute with your employer.
Because companies are going to base salaries on collective agreements with the union which are usually lower compared to the salary high paying jobs have. At least that's how unions work in my country. Unions are powerful because they can call for protests and employees who are in a union cant get laid off due to joining the protest. But its not worth if the job already has way better working conditions than like 80%…
Even without unions Europe wouldn't have US tech salary levels, those numbers come from other market dynamics.