I was in my Jeep J10 pickup some years ago on a street like that. I was stopped preparing to make a right-hand turn, which had a marked uphill tendency.
The truck would not move. It had "Warn" locking front hubs which were unlocked, it was empty, and the right rear tire had zero traction on the leaves. When I let out the clutch, it literally just sat there with the rear wheel turning as if it were on rollers.
There was a car behind me so I couldn't back up. I had to jump out with a sheepish wave to the guy behind me, lock the hubs, and jump back in.
Yes, wet leaves ARE greasy. A bike will go down on a layer of wet leaves in a second ....
Lannis