There are lots of things that use right-clicks on a PC in the game, usually explanatory in nature. In addition, right clicking on many things without anything special attached to it would show the usual "Save page as, Show background picture,..." menu that's not useful at all for the game. So this has been disabled and replaced with specific actions when the game supports it.
Not using my tablet often in that way, I have no idea how inter-program data exchange (like with a password manager) is usually handled on a tablet/phone. If it works via long press or something similar, it might indeed be a good idea to enable that on the login page.