I remember how for the longest time they held off, on the premise that a badly written VST could crash the DAW and users would blame Reason rather than the VST. They relented when technology and programming techniques got to the point where they could sandbox the VST running in Reason such that if the VST crashed, it would only be the VST that crashed and it would not take Reason down with it. I, for one, am glad they got that sorted out. They also worked out how they could provide the kind of back-panel interconnectivity to VSTs that native Reason devices and rack extensions already provided. The modern Reason rack is almost a modular synth system all on its own.