Bicycle undercarriages (B-47, B52, Hustler, Vautour, Harrier etc) are creations of the Devil (so far as take off and landing handling goes) but still the better way to go in some circumstances. With all except the Harrier I have little doubt the decision was taken to avoid a very long pair of main tricycle legs, with attendant problems in retracting them into thin wings plus the need to free up the fuselage around the CG for bomb bay use, rather than as a home for two narrow track tricycle legs. With the Harrier, it was a bit of the long leg thing as above, plus the space needed around the CG for the donk and keeping the splayed hot rear efflux from blowing directly on a pair of tricycle legs – well their tyres anyhow.