By this point they've figured out that in the audiences' mind, the name of the series is "Rambo", not "First Blood".
Having made a pile of money off the first two movies, a third was created. The result was something halfway between its predecessors: less story and more action than the first, but without the extreme disparity in the second. Still, the point is to build on the enduring memory of the first movie: strong action hero takes on enemy forces, practically single-handedly, and wins. That the final enemy is what seems the whole Russian army is, indeed, going a bit far.
Here's hoping that the fourth installment, recently released, manages to get the high action and meaningful story due a big-budget movie descended from the first Rambo.