That's because unions are an integral part of the way many of the countries socio-political systems work. In Norway, for instance, the trades unions and the employers get together once a year to hammer out what is called tarriflønn, essentially the going rate for each broad type of job. The state provides a referee for the meetings whose job is to keep them on track and to encourage both sides to compromise. Unions and companies work together rather than fight each other, most of the time.
But this can only work if there is a broad consensus that we are all in the same boat and that we will all be better off if we work together.
The attitude, that appears to be common, in the US that employers are always exploitative, employees are always lazy and thieving, that the government is just a parasite, and that the aphorism "Good enough for government work" is a synonym for delivering shoddy work means that no one trusts anyone so you end up fighting all the time.