The strength of animals is vastly underrated in D&D. Many animals are far stronger than most people imagine, far beyond max human or even low-level superhero strength such as Captain America potential. It's applied differently, a grizzly bear doesn't need to show off to his weight lifter bros. On the other hand they can rip your car door off if there's something tasty inside. Of course I also think that grizzly bears' CR is also too low, but that's a different issue.For an animal a bit closer to a Human, and one of our nearest cousins, a Silverback gorilla is around 5-9 times stronger than a Human, and can lift 4,000 lb (1,810 kg) on a bench press, while a well-trained man can only lift up to 885 lb (401.5 kg).
Apes have a Strength of 16 (size Medium) and Giant Apes 23 (size Huge) so you'd likely have a Silverback Gorilla somewhere in the middle of those two game stats, with 'Apes' likely representing something like an Adult Chimpanzee (also a crazy strong animal).
But people want to maintain the Tarzan fiction that a human could wrestle a gorilla and win. That, and the simplified math and calculations start to fall apart at higher levels of strength. So actual strength is far higher, applied strength in terms of what the game cares about is far lower.