To be able to open the door easier (let’s say, a fire) and the knob could make some jobs more harder, like moving huge stuff from one side to another. That’s all. Should be true that can be easy to clean, but that it’s a side effect of its original purpose.

Smooth surfaces such as polished metal have fewer areas to harbor bacteria compared to the fibers of a wooden door, for instance. In addition, a flat surface is easier to clean than a round knob.

Another benefit is that some metals have a natural antibacterial property toward bacteria organisms on their surfaces.

Doors that push open are a lot more amenable to panickong people who need to get out in an emergency. You may notice that a lot of these non-latching or push-mechanism doors also swing out towards the exit.

ADA prefers them to doorknobs. Back in the day when hardware conventions started, it was to show that a place was free to walk into without a barrier, i.e. open to the public. Think about saloon doors, kind of a modernization of that. Not to mention you can open it with your back and they’re cheaper to produce/buy than knobs and handles.

They say brass can sanitize, but assuming it’s not that…

Its easier to clean and will prevent wear on the door itself.

Business doors are often sprung to close automatically - possibly a fire regulation thing. So they don’t need a latch to stay shut. A knob or handle is often the way to release the latch.

Flat plates vs say, a bar to pull can also naturally communicate push vs pull if it only opens one way.

Trying to work a doorknob with your hands full of bags is a hassle that nobody needs. How many times of people banging into a door that didn’t properly unlatch would it take before something/someone gets damaged?

Why do some houses have a knob where a push plate should be?

I assume it’s an access plate to service the door mechanism.