Gotta remember - Asphalt is simply the leftovers from oil refining mixed with aggregate (rocks).
Crude oil is basically a mix of a bunch of different hydrocarbon strings. Some are very short, and some are very long.
In refining, they separate these strings. Shorts end up as things like D-Limolene and other aromatic petroleum products that are typically used as solvents and/or fuels. The next step up are the medium lengths that typically go into greases and oils we are all familiar with.
The super long strings that are left over are what I'm referring to as "the left overs". Thick, nasty, sticky, black tar looking [censored] that is used in a few limited applications. Asphalt is one of them.
Back in the day, these leftovers had higher concentrations of the short and medium strings in them. This led to a higher quality, and longer lasting, asphalt. As refiners have gotten better at pulling all those more expensive molecules out, the leftovers became worse. This made them perform worse at their job as "glue" in asphalt.
Similar to all oils - asphalt oxidizes and degrades under heat, UV light, and other conditions. Then - when you spill a refined oil on them - it starts to want to mix with the "leftovers". The asphalt binder begins to loose some of it's binding ability since it's effectively having it's viscosity lowered. Like someone else said their father said, "Like dissolved like".
To clean - oil dry, sawdust, kitty litter, and some elbow grease.
PLEASE DO NOT WASH OILS AWAY WITH WATER! Even when they are encapsulated in sufactants due to soap being used - they are still bad for our environment. A lot of the old guys here will probably roll their eyes - but it's serious stuff.
DO NOT WASH OILS AWAY WITH WATER! DO NOT LET OIL GET INTO YOUR GROUNDWATER OR SEWAGE SYSTEMS!!