There are more games on the illegal file sharing sites from Steam than there are from itch.io - but they exist from both. So going the Steam route won't protect you.
Large sites like Reddit allow the illegal file sharing sites to promote their business and they refuse to take down the links. Those web owners likely make more money from the games than the individual developers. These sites would not get as much traffic if they weren't allowed to actively advertise their websites on Reddit. And yet, Reddit bans self-promotion. So the person who steals my game can freely advertise it and I can't. I refuse to visit / support Reddit, that's all I can do - I'm pretty sure nobody at Reddit cares.
When I was making 3D graphics I was selling on average 6 to 10 copies - and approximately 60 people were downloading them from an illegal file share site. I didn't make enough money to make it viable and quit making graphics. Now I have the same situation with games - it's not viable for me to make games - and I don't have the time or power to fight all the sites that illegally have my games on them.
So a lot of people have the impression - well at least someone is playing your game - or enough people buy it to make it viable - it doesn't matter if we steal if - but that isn't true -and it has a ripple effect - the developers don't make money, then the software developers stop making money, places like Steam and Itch.io make less money... Would you go to a supermarket and steal a candy bar and eat it and tell the owner - well at least someone likes your candy? Why is stealing my game any different? I also have overheads, I also had to buy the ingredients, in my case the game development software, I also had to wrap it and package it ...
But my only advice is - shrug it off. It's going to happen and there isn't anything we can do about it, right now, every industry struggles with it.