hi! I also play a bunch of Magic and I think you're looking at this from a poor perspective
Showdown is W A Y different from an LGS. Interactions at game stores are usually a lot more personal; you're sitting face to face, interacting directly in front of a bunch of other people. One bad attitude can ruin an entire event or even drive people away from the store altogether, so calling someone on shitty behavior makes a significant impact. Showdown meanwhile has literal thousands of active users at a time. Being entirely online makes it a far less personal experience, and while a rotten apple can ruin an experience, it also affects a fraction of a percent of the active userbase. Name shaming doesn't even do all that much when someone can just switch usernames and get on with their life, or just count on people not really seeing it. (I can guarantee you that maybe 10% of the people who will battle this person will see your post.)
While some dude in the 1100s might "get away" with it, toxic behavior does frequently get called out within the various subcommunities on Smogon and PS, where it's a lot more likely to impact a significant number of people. It's the sheer volume of Pokemon Showdown that makes this sort of name-n-shame pretty damn ineffective outside of those communities.
Forgive me for my midnight brain dump, and also keep in mind that you can always call in a global staff member (like me!) to deal with situations like these - unlike Modo/Arena, Showdown actually has active moderation staff! Now stop slow playing or I'm calling a judge