Why is a coulomb not a fundamental unit but an ampere is considering that a coulomb is more ' fundamental '?
A fundamental unit is defined as
one of a set of unrelated units of measurement, which are arbitrarily defined and from which other units are derived.
As per wikipedia:
The SI unit of charge, the coulomb, "is the quantity of electricity carried in 1 second by a current of 1 ampere".
The coulomb is defined using the ampere, so per the definition, it's not fundamental. The ampere is, because it isn't defined using other units.