Unlike the major leagues, league clubs in soccer (and in most other sports) belong to national federations that in turn belong to continental and world governing bodies, that in turn set rules and regulations for the sport. Since the invention of international representative competition by the English Football Association in 1872, it has been an accepted rule of these federations that clubs must release players without compensation to play for the national team. Given that national and international broadcast rights are now valued in the billions of dollars, this has become a hugely controversial issue. To be clear, players usually want to play for their country, either out of national pride or with an eye to endorsement opportunities created by representing the country. They are also paid, but generally not that much compared to their club salaries. The governing bodies and national associations share out the money for development of the "grass roots", and funding their global operations. The clubs get nothing, even though their employees are often injured.
The G14, an association of big european clubs formed at the end of the 90s, launched a challenge against this regime in the Swiss courts (FIFA, the world governing body is based in Switzerland), but seemingly got nowhere. They have now formally joined proceedings in Belgium where Royal Charleroi, a relatively small club, has challenged the regulations that oblige clubs to release players without redress.
If you're wondering why the clubs don't just secede from the national federations, the answer is that (a) many clubs want to stay within the system, they just want a share in revenues generated by players they employ and (b) breakaway would involve setting up a rival league, and US experience shows this is not easy. However, in recent years the G14 clubs have become so financially dominant that a breakaway is certainly on the cards. A european superleague formed by these clubs and their allies would certainly be more balanced than most domestic championships, and would enable to the top teams to play each other more regularly. With the broadcast rights to the Champions League up for renegotiation next year, we may be approaching a watershed in European football.