Open top Formula style racing cars allow a drivers head (arguably the most critical part) to be exposed to impact from foreign objects. Since there is not really anything to see from a driver action point of view these days unlike in the 50's and 60's, designing cars with closed "Fighter jet" style canopies really wont detract from the spectacle
Why is this important?
Changes to these regulations by the governing bodies of the series, will mean that deaths from incidents such as Henry Surtees and Justin Wilson will be significantly less likely.