They actually banned ALL professional sport, it's just that other sports didn't have the weird psycho trauma around professionalism as rugby. It is also a key reason why France doesn't have any inter-city derbies in football that are features of every single other country's league.

These days rugby union & rugby league are considered basically separate sports with a common origin, akin to Australian Football & Association football.

At the time this was not really the case, particularly in France, and rugby league was considered the professional version of rugby, with rugby union the amateur version. It was only in 1922 that the governing body of the sport in England changed its name from the "Northern Rugby Football Union" to the "Rugby Football League". Within France rugby league only started in 1933, after their expulsion from rugby union's Five Nations the RFL approached Jean Galia an extremely good player who had been banned for professionalism & poaching players to create a touring team of other banned players, the tour was a success & the game popular.

Galia was good at promoting the sport & the main French union hamstrung by being cut off by the British but really wanting to get back in with them, so rugby league was popular & growing. There were c.160 rugby league clubs & 560 rugby union clubs at this time.

There is evidence that personal enmity between Galia & senior people in rugby union who were sour at him approaching their players played a large part in the particular treatment of rugby as a single game & therefore the confiscation of league assets for the use of union teams.