Players who have visited any of the larger player forums tend to be quite aware of this.
The sad part with poker is that there are some unscrupulous affiliates who, in an effort to steal players signed under other people, will promise them rake back or other rewards and get them to go against all T&Cs to sign up under them, even if a second account at the same place is needed.
I such a case, and with increasing frequency, these players are victims who have been talked into it by some unethical affiliate.
Of course, poker players can turn into bonus whores just like casino players, and these often use multiple sign ups to collect multiple bonuses.
That appears to have been the case here.