Because not every plane is the F-2. For many that +50% limit is genuinely needed for them to fully use their limits. Also countries do usually put the operating limit a good bit below the true structural limit. So it makes sense to exist to an extent. I still personally agree +50% is too high.
If i had to guess +50% is a holdover from when the game was props focused, as while not a reasonable number for modern fighter jets, +50% is actually a relatively normal structural limit for many props, particularly Japanese ones.