There was no conspiracy that caused the demise of the Rotodyne. Yes, the tip jets were noisy. But the aircraft still required fixed wings and turboprop engines for cruise flight. The benefit provided by the tip jet rotor for VTOL operation of a commercial passenger aircraft was not worth the added complexity. There was plenty of space available to build conventional airport facilities.
What happened with the Rotodyne was no different than what happened to the Concorde. Ultimately, neither aircraft design could convince operators that it provided sufficient economic value.