It works because you have the juice flowing into the CRT maxed out (full brightness) and when you yank the power cord the CRT desperately is searching for more juice to keep itself alive. Because of that, it grabs all the available juice it can find in the electronics powering the CRT until they run completely dry. They run dry very quickly because the CRT is maxed out in brightness.
If you are dissatisfied with that layman's terms explanation, think of it in terms of a load on a capacitor. There are certain types of capacitors called "memory capacitors" that keep clocks or memory alive (for several days or weeks, until the capacitor runs out of juice) when the main power is cut. These caps can keep the circuit alive for a long time because the circuit attached to those caps sips very little power in the first place. Now compare that exaple with the capacitors in the power supply of a Mac Pro computer. How long do you think those caps can keep the computer running after you yank the power cord on it (however big, fat and physically large they may appear to be to your eyes)? Milliseconds at best. That's beause the computer requires so much more power thank those capacitors can supply. The computer drains all those PSU caps almost instantly when the main power is cut.
Simply put, the CRT when brightness is cranked up all the way draws more power than any residual power in the computer (after the power cord is yanked) can supply. Because the CRT uses up all that residual power in a few short milliseconds, there is nothing left in the video circuitry of the vintage compact Mac to shock you.
If you are dissatisfied with that layman's terms explanation, think of it in terms of a load on a capacitor. There are certain types of capacitors called "memory capacitors" that keep clocks or memory alive (for several days or weeks, until the capacitor runs out of juice) when the main power is cut. These caps can keep the circuit alive for a long time because the circuit attached to those caps sips very little power in the first place. Now compare that exaple with the capacitors in the power supply of a Mac Pro computer. How long do you think those caps can keep the computer running after you yank the power cord on it (however big, fat and physically large they may appear to be to your eyes)? Milliseconds at best. That's beause the computer requires so much more power thank those capacitors can supply. The computer drains all those PSU caps almost instantly when the main power is cut.
Simply put, the CRT when brightness is cranked up all the way draws more power than any residual power in the computer (after the power cord is yanked) can supply. Because the CRT uses up all that residual power in a few short milliseconds, there is nothing left in the video circuitry of the vintage compact Mac to shock you.