My guess on why this is well-received is that the immediately obvious consequences are positive. You don't have to go to work and you're allowed to reschedule flights when you're sick. Most people have had to work while sick, which is miserable, and a lot of people have been sick on trips, which pretty much ruins them. I don't think the reasoning extends much beyond that.

But when you talk about indefinitely quarantining people with incurable diseases, that feels like persecution of a minority group for something outside of their control, which everyone knows is Bad™.

Also, the phrasing of the quoted comment doesn't sound like a mandate.

...why not also require people to be able to reschedule flights if a doctor certifies they have a contagious disease?

I predict you'd get a different response if the proposition was to forbid people from flying while showing any symptoms of being sick and fining people for sneezing on an airplane.