Some people are throwing used masks everywhere. Why are they so uncivil?

Because they're disgusting individuals who clearly live in their own filth if they're incapable to know how to use a rubbish bin.

Not many in my neighborhood, but a few.  First of all, it depends on the normal baseline of how much littering there is.  Second, a mask on the ground is less likely to get cleaned up by a casual onlooker, for fear of infection.  Same as anything else considered unclean, like used kleenex or toilet paper.

I have been wondering the same thing, see them scattered around quite a bit when on 

my bicycle rides. How difficult is it to carry a plastic bag and dispose of them properly?