Two things

First, humans are simply much larger and heavier, and have much more mass per surface area to try and oxygenate - and it must travel much farther to reach the critical organs. It’s not a very efficient system so most amphibians are very small and many supplement with lungs, gills, and/or tricks to increase surface area.

Second, if you’ve ever met a frog you may have noticed that they spend 99% of their time motionless staring into the abyss. They’re cold blooded and have poor oxygenation capacity, and so have very little metabolic energy reserve to spend. They move infrequently and tire quickly. Humans are tireless hyper-endurance athletes by comparison. We can move all day and burn oxygen at a much faster rate - but need much more food to do so.

That’s one of our evolutionary advantages, even by warm blooded mammal standards humans are tireless athletes. We’re not the fastest or the strongest, but we can pursue for hours like a horror movie slasher until any prey is absolutely gassed.