We don't need it, but it's too late now to drop it. Going back the the Joint Strike Fighter program circa 1993, the primary requirement for the V/STOL "B" model came from the USMC. They had an institutional fear stemming from experience in WWII that they couldn't depend on Navy fleet carriers for the close air support mission so they insisted on having that capability organic to amphibious ships (which lack catapults and arrested landing equipment). Originally that mission was performed by the AV-8B Harrier, but they (correctly) recognized that it wasn't survivable against modern air defenses. Hence the requirement for a 5th-generation replacement. The Marines had a lot of political influence in Congress at the time and were able to get their way. Requirements from international program partners including the UK and Italy who wanted to pretend that their crappy little mini-carriers could still be relevant also played a part.
Today the notion of conducting an opposed amphibious assault looks increasingly unrealistic. Even third-world terrorist groups now have drones and guided missiles that could massacre the connectors and transport rotorcraft. The F-35B can survive but there won't be any ground troops alive to support. So it's original reason to exist has largely vanished. And the sad thing is that the pointless V/STOL requirement forced a fat single-engine airframe on the entire program which badly compromised the "A" and "C" models in terms of reliability, range, speed, and payload. Oh well.