This could have been a great idea since the tunnel was built in the 70's under the F train; but the MTA is actually just the agency that can borrow money with 6 companies under it, including MNR / LIRR. As I understand it, the railroads get federal funding separately and if LIRR joined the MNR tracks into GCT, they would have been forced to split federal funding (and lose money). So LIRR was forced to build a whole new station under GCT, hence the walk. Such a shame and wasted opportunity for petty politics :/