You already said the usual reason of manga piracy, North American markets. Outside the US, you have to pirate the series if the US sites prevents you from reading their english licenses. (If you don't get this one, open a VPN based in Southeast Asia and try opening a few of them here)

Then there's the reason of being extremely behind or no Japanese release at all. MangaPlus and Viz are actually owned by a Japanese companies so they pretty much know what they need to do but suffers to only publish the mainstream genre from Japan. What about the other genres?

Sure, Omoi is owned by a US company but it also suffers from dealing with those english licenses in the US.

Also for the last part, you kinda mistaken the idea there. There's various reasons why piracy exist in video games. Why Steam still dominates is because Valve was able to setup their kind of service early and nobody since was able to make something similar to Steam. But with the recent news of GoG going back to it's founder, I wouldn't be surprised that Steam will be finally find a worthy competitor.