Suppressed Revolvers

[Mazryonh]

I'm confused. If a sealed cylinder gap for revolvers means that more of the powder charge's gas can be directed to the bullet, rather than being wasted by leaking out the sides of the cylinder, why hasn't the sealed cylinder gap then become standard?

I hear some novice shooters get powder burns if they place a hand near the cylinder gap when firing. A sealed cylinder cap would likely eliminate this hazard.