we don't have 19 in service because those are light assault ships. they aren't going to project a lot of power
there's also been the idea of mobile base platforms, multiple ships putting down huge stabilizers for support and connecting to one another, capable of launching and landing our biggest aircraft. they've put that aside as it's too spendy. so we getting merely the carriers.
the 10 they are building is to replace the 10 in service. these things take a long time. the first will be replacing a 55 year old ship.