It's pretty easy, i got banned from a couple of subs for being left-wing (apparently calling out brigading from far-right subs was against the rules).

But i got a sitewide ban because I used an alt to ban evade (can't remember the exact post, but somebody was asking for advise wrt to COVID in a legal sub (I was originally banned for for encouraging a user to get funny but illegal payback on their neighbors), and it felt urgent enough that I was fine getting banned.).

Once you get a siteban, trolls will flag report all your posts even on subs your not banned from, or at least whenever I brought up that r/UKpolitics is modded by a literal fascist, I'd get a new site ban for "ban evasion", to the point where pretty much any encounter with a far right troll or YIMBY would get me a ban.

The admins also seem to work very closely with certain moderators, as was shown when they leaked a trans employees information to TERFisland subs.

So while powermods can't get you a sitewide ban, some have the ear of the admins who can keep an eye on you until you break a sitewide rule.

And on a site which has alt-right subs, it's hard to at the very least walk right up to the line on the rules wrt treating all commenters like humans.