You know, I live in the land of big Maple trees and had one in the back yard that was around 175' tall and shaded the whole back of the house pretty well.
They dont drop sap...Ever... But Aphids get up there occasionally and they drop Aphid Poop down all over everything. This stuff is kind of clear like sap, a little sticky, but NOT real tree sap of course.
The Aphid poop will come off way, way, easier than any tree sap will, so Im thinking that is what is falling on your car.
Real tree sap is resinous, sticky, dries hard and is almost impossible to wash off easily.
I have to use stuff like Goof-Off on the end of a Q-tip to get the sap off.
If you are washing the stuff off your paint with whatever soap, I can pretty much say that this is not tree sap.
Be happy it is not !

Aphid poop is like bombs from above that are never ending until they get eaten up by ladybugs, birds, etc.. It is awful....
Certain conifer trees dump sap but a Maple is a deciduous tree and not a conifer.
Like everyone else has said, you need to move and not park there anymore or get some kind of shelter over your vehicle/s, or just resign yourself to deal with this and eventually, it will stop.
Good luck !
Dan F