Yellow posted...
I find it kind of badly designed? Capacitors should discharge themselves on shutting off?
I think they do, it just takes a long time for a capacitor of that size to fully discharge, and that means there's a dangerous amount of energy left in it. It's not a design flaw so much as an inherent limitation of how the physics of electricity work. I expect that to discharge it faster than that (without going through the process of connecting a dozen heavily insulated things to various grounds before shorting it), the microwave would have to have a process you could activate to block it from charging while still being plugged in, then have the microwave run until it mostly drained. You'd have to do that before unplugging the microwave, but theoretically it would be safer.
In practice, though, I don't know that you could guarantee that such a process would actually discharge the capacitor enough to eliminate the risk, so for liability reasons it's probably better and definitely easier for manufacturers to just not offer the option and instead give a blanket advisory to have an electrician service your microwave instead of DIYing it. As it stands now, they say not to do it, so that puts the onus on anyone who does want to do it to research it themselves and figure out how to do it safely and absolves the manufacturer of the responsibility.