The answer, as I am sure you know, is that they like the staus quo of sucking up tax money and providing three automatic electoral votes to the Democrat presidential candidate before the polls even close.
Sure, they would like to have two voting senators and a representaive as well. But good luck with 3/4th of the state legislatures going along with that one.
By population it should be 4 electoral votes, especially as they pay 100% taxes. I am not sure what tax money you think they are sucking up. It is unlikely that Maryland will want retrocession or that 3/4ths of the State would approve statehood. Thus since all the DC taxpayers pay 100% taxes but only have 2 out of the 5 elected representatives that everyone else has, then just let them pay 2/5ths of the Federal tax. That would be fair.