So Like I’m Wondering

I have for a while been wondering about two things I read in Science class so long ago. If you were to scale a human up to like 20 feet tall, their bones would break under the weight of the muscle and bone weight, mass would grow exponentially and the strength of bones would not.

Elephants look pretty stocky for being as large as they are, just an observation. Big heavy solid feet, not those dainty toes that the big running predators stood on.

Could gravity have grown stronger over time? Is there any science that can offer clues to the an possible changes to earth gravity in the past? This is the first thing that popped into my mind. I dunno, seems unlikely.

How did dinosaurs get so big and not suffer the problems that bedevil giant humans?

I did get one good answer when I asked this on a forum, but it is just more interesting mystery that answers.