I was referring more towards the fridge nuking scene, but then again, this is the same series that has tubing down a mountain from an airplane.

I actually like the alien reveal, and it's telegraphed throughout the movie, so it's not like it comes out of nowhere like some people claim. I also think it ties in well with the villain's mysticism as well. With the nazi's hunting for the arc or the holy grail made sense because Hitler and other members of the SS were obsessed holy relics and did dabble in trying to evoke divine powers. The Soviet Union on the other hand was mostly secular, but was experimenting in psychic manipulation and thought control all the way up until the 80s. Meanwhile the whole space race between the US and USSR breathed a fascination in extra terrestrials very similarly to the phase Americans went through. So having a psychic obsessed villain trying to seek out alien artifacts that could unlock those abilities makes sense.

It's the difference between believing the pyramids were built by ancient Egyptian gods, and believing they were built by aliens. It just doesn't fit the swashbuckling source material the other Indiana Jones movies were built on. Same reason time travel didn't work as a plot device. It doesn't fit the genre.

I know almost nothing about the Fast & Furious franchise, for instance, but I'll bet if aliens made an appearance there it would be met with scorn as well, but they have no problem doing physics-defying scenes all the time.