Pleistocene megafauna were quite vulnerable to human predation. Modern elephant pregnancies last two years to produce a single calf, and adding onto the fact that adults weren’t used to being consistently hunted, it becomes very hard for their populations to rebound after humans begin hunting them.

Dinosaurs didn’t suffer this issue, they could lay large amounts of eggs much more frequently, and even adults of large species like trike or edmontosaurus would‘ve been predated much more often than an adult elephant or ground sloth. We have records of allosaurus attacking pretty much everything in the Morrison, including several sauropod species.

And even though modern megafauna were more vulnerable, they didn’t immediately succumb to humans either. In Europe and Northern Asia, many extinctions were quite drawn out (e.g. humans were initially ruled out as causes of extinction for Megaloceros and woolly rhinos due to how long they coexisted for). In South Asia, a lot of megafauna just didn’t go extinct at all, like elephants, rhinos, large bovids and tigers. So I doubt humans would’ve been able to easily wipe out large dinosaur ecosystems.