As was said humans are used to natural levels of radiation and other fields. Not artificial ones. Not any level of radiation. Or you'd be an immortal superbeing able to fix Fukushima Nuclear Power Plant with your bare hands.
"not feel much" doesn't mean it has no effect on your body. People often don't feel cancer until it's too late.
You don't think that at 2.4 GHz the danger is suddenly switched on. Like it was safe at 2.39 GHz and then BAM, microwave, don't put your head in here! The danger slowly rises with the frequency, power, proximity of the source, etc, etc. Even at 1900 MHz it may be not safe. Even if the temp rises just for 0.0001 degree. That's why that test is nothing. Take a bunch of animals and put it to a lifetime exposure to cellular radiation, give them phones, cellular enabled watches, wi-fi routers, etc, etc and at the end of their life we'll see the effects. But no one is going to do that. People themselves are those animals.