Why did Apollo Creed lose to Ivan Drago so easily?

It's plausible that a young fighter would utterly defeat an aged former champion, yes.

Would a guy that was effectively making his professional debut be able to be so dominant over an experienced former world champion that he'd kill him? Probably not in real life. But Drago was bigger, younger, stronger and had been doing steroids. (Whereas Creed supposedly hadn't.) So it's not entirely impossible. Especially because Drago trained properly, whereas Creed had been taking it lightly expecting an exhibition bout.

Best just think of it as a film. It was setting up Drago as a threat.

because he spent all his energy dancing before the fight

1. Creed didn't take the fight seriously and didn't train properly.
2. He vastly underestimated Drago (who was a competent boxer) and thought he would box circles around him.
3. Drago was on super-ultra-red steroids. Thus anything he punches he destroys, except iron.

Even if Drago wasn't on steroids, Drago would have won the fight because of reasons 1 and 2, although it most likely would have gone to the later rounds considering Creed's stamina and chin.

It's poorly written.

Apollo was not in his peak and had not fought in 5 years also we didn't see any of his training but he was still in good shape not ring shape.

But what people forget is this was an exhibition a lot of what Drago did would of resulted in a DQ also the whole him not throwing punches being hit freely by Apollo was dumb it doesn't matter who you are you wouldn't do this an ex world champ would put you on the floor.

Some people mentioned Apollo stamina well we dont know do we we never saw any of his training and age doesn't mean you can always go longer or shorter experience is very important also again this was an exhibition not a full fight so the rounds are shorter in length plus not as many of them.

Apollo had been retired for more than 5 years, he agreed to comeback to fight Drago for an *exhibition* fight.

His mind was set on just putting on a show (have fun in Vegas of all places, along with James Brown introducing him) for his fans and fans of the sport.

I've seen some real world exhibition fights, they usually wear those padded helmets, more protection and neither fighter hits at 100% to prevent the other one from getting harmed.

This was definitely unexpected.

Drago's mentality was somewhere else... he was not an athlete, he was a psychopath.

OLD & COCKY VS. YOUNG & VICIOUS.

The answer to to OP’s original question is: 1850 lbs of pressure per square inch.