A few reasons, it's illegal to question the Holocaust in many European countries. The co-chair of the AFD said that the Nazi era amounted to bird shit within the context of Germany's otherwise long and successful history. Saying that might land him in jail. Not being differential enough to the jews is considered hatred. Also, you don't have much reach in traditional medias, and most right wing content online focus on American topics and views. So if you are trying to win over these people, you'll try to espouse views somewhat close to what the biggest right wing voices espouses. You'll be influence by Shapiro, Hannity, Crowder, and the GOP in general. Imo, that's why Le Pen is the further off the GOP because French are the least likely to speak English and mimic American values. And that's also why once Trump expressed ideas that are less inline with the GOP, talking about nationalism, border, trade, etc. these European right wing parties boomed. But ultimately, the reason why they don't is because if you are overt about it, they'll try really hard to ruin your life and are quite likely to succeed. They will weaponized the justice system to destroy you, your family, and your loved ones.