i can't even fit 300gb on my internal drive, unless it was the only game installed.

That's why they're inflating the size like that, because they want to occupy as much space as possible and be as much of a pain to reinstall as possible so people get rid of their competitors and keep them around forever instead. It's a toxic competitive adaptation that's been getting progressively worse over the past decade or so since the strategy has worked out for them so far.