I agree. Would it be so hard to be able to have the story continue.
Yes, yes it would. At a bare minimum, if you allowed freeplay after the end, you'd have to remove all NCR troops and autofail all NCR quests (any ending except the NCR one), remove all legion troops and autofail any legion quests (any ending except legion), completely revamp the power structure in New Vegas (Yes Man ending), and remove the Kings (House ending.)
You'd then need more quests and many more lines of dialog to convey the situation changing.
If we had a game that allowed freeplay after the end without urinating all over the ending, we'd end up with the game coming out in 2012, if that.
Meanwhile, the way we have now, where there's this
big huge message box that cannot be skipped or ignored allows all the freeroaming benefit of freeplay after the end with none of the downsides. Not
one single person who's ever advocated for FP after the end has ever explained to me why the solution we have is a bad one.