Phone calls are not the feature they would be most likely to disable. You're more likely to have passengers talking to you with their phones stuck in "driving mode" as they can't use them to quietly pass the time playing a game or reading or browsing social media or whatever else the driver shouldn't be doing with their phone.
Unreal is "source available", not Open Source. There's a big difference. With any Open Source project you can legally fork the project, distribute your custom version of the code, create a community around your variant... "source available" has none of that. The Unreal EULA is more permissive than most game engine licenses (with the obvious exception of Godot) but it still comes with plenty of restrictions. For example:
You are permitted to post snippets of Engine Code, up to 30 lines of code in length, online in public forums for the sole purpose of discussing the content of the snippet or Distribute such snippets in connection with supporting patches and plug-ins for the Licensed Technology, so long as it is not for the purpose of enabling third parties without a license to the Engine Code to use or modify any Engine Code or to aggregate, recombine, or reconstruct any larger portion of the Engine Code.
Which pretty clearly does not satisfy the Open Source Definition.
"Normal world" knowledge often does play a part, but more than that I think part of the draw of isekai stories is that the audience can more easily empathize with a character originally from our world trying to make sense of the fantasy they find themselves in than characters who are from the fantasy world and thus don't find the setting particularly special.
It's not like straight fantasy stories have died out, though. In the current anime season alone you have Sousou no Frieren, Goblin Slayer, S-Rank Musume, and Mahoutsukai no Yome—and no doubt several more—where the protagonists are native to their respective fantasy settings. That's not even counting ones set in fantasy VRMMOs, which aren't exactly isekai either.