>>97384578A mix of factors
until relatively recently, communications across the ocean weren't exactly easy-peasy. That's why even South-American stories weren't really known in Europe until the 90s
Disney USA basically stopping making comics.
Protectionism, both sides: people prefer keep money running in their side of the pond. Possibly more in Europe than USA.
Alleged different local tastes: this might be truer for the USA side, as even now IDW has to localize and change dialogues, even minor things, and colors to fit the assumed taste of their readers
Mix various amounts of those and you get the divide.
