And better yet, why not have all of the strip connected in one cell? Assuming one has a pretty good gaming rig, there's no reason one's computer can't handle it (at least theoretically). Personally I'm just not a fan of "forced" loading zones, like doors to interiors (especially ones that aren't interiors!)

Theres like 4 of those mods that make the strip one cell. The problem is the npcs dont react right when you do it. Extra scripting required. Not sure if anyone has fixed that yet

Because from a development standpoint, it is completely stupid to make 2 versions of the same area just for those who have better computers. The strip is not connected to the rest of the wasteland for performance reasons. The strip is divided for performance reasons. Those with good computers are in the minority as the developers had to consider console hardware limitations and the specs of the average user's computer.

Not to mention, it's easier on the AI Packages.

It'd be doable, but it'd be a compatibility nightmare and wouldn't actually achieve anything as the Strip would still only have one entrance with a security gate in front (removing it would kind of defeat the whole "The strip is separate and secure" deal), so you'd have to pass through a door anyway.