I think what you mean are, Why have the FBI and DOJ only focused on traditional Catholics? There are more numbers of conservative Protestants
The first question presupposes that the powers that be are not focused on conservative Protestants, but which I am sure they are. However TradCaths are more easily focused upon since their sects are more distinct than conservative Protestants, as the later are spread out among numerous denominations and churches. Somewhat dated relevant stats: https://peacebyjesus.net/rc-stats_vs._evang.html
They are just the first of all the rest this is going to happen to. Pretty soon any image of God will be deemed offensive and illegal.
It’s coming for them all, they are just starting with the Catholics first.