On my phone, the wall charger is twice or 3 times faster than the
one in my car. Why? (I'm looking for the technical details)
The answer is probably You! That YOU are not willing to pay more than
a certain amount for a car charger. (When I say you, I mean consumers
in general).
Would you pay less than $20 for this... Probably a lot of people
would.
Would you pay $80 for this... Probably most people would not.
Anyway it all has to do with cost/price. Cell phones need a voltage
other than 12 volts DC car voltage and other than 120 volts AC from a
house.
It is inexpensive to convert AC voltage to a different voltage and
also provide a lot of power.
But it is quite expensive to convert a DC voltage to another DC
voltage and also provide a lot of power (amps/watts/charging time). If
the amps/watts are small, less expensive components can be used. And
the total price for the product will be less.
Something similar are car "inverters" which create 120 volts house
electricity from a car battery. Notice as more amperage/wattage is
provided by these gizmos, the box gets larger and the price goes up to
hundreds of dollars.