Why is it not more sturdy?

It's always toppling off, and my dinner with it.

Seriously, you'd think they would have a way of securing the plate so it is secure and also having the ability to remove it for washing.

Does anyone have a technique is to keep it on, or to put it back on?

Thanks.

It's perhaps one of those things you should've checked before you bought the microwave.

Mine's got a big sturdy, plate that sits on a turn table. Not had any problems with it tipping and it's easy to take out to clean and put back.

Never had a problem with any of the microwaves we've had.
Inside, in the centre of the bottom of the microwave, is a "spigot" and if the glass plate sits on that correctly, and on the turntable, you cannot rotate it by hand, other than a few degrees each way.
If yours is "falling off" (falling off what?) it's not been placed properly.

Does it actually rotate when cooking?

Yeah it rotates but as I lift the dish out the plate falls off.

I suppose you get what you pay for.

Why are you taking the glass plate out ?.
, I would just lift of the plate or dish. I only lift out the glass plate to wash it.