I travel to different countries with my phone and would like to be able to charge it.

I dont travel with my toaster/kettle/washing machine

Small appliances rectify AC into DC before using it and therefore what you end up with is a DC supply that can support multiple input voltages and frequencies.

By contrast, larger appliances typically use the AC directly. A motor is designed to be able to connect directly to local AC power, and the voltage is quite important and so is the frequency, because a change from 50 hertz to 60 hertz will make a motor go much faster and a change from 60 hertz to 50 hertz will make a motor go much slower, and resistive loads such as furnace elements which are designed to be able to be connected directly to mains power our engineered with a specific resistance.

For motors changing frequencies, the way you would end up having to retrofit such devices is to rectify the DC signal and then reconstruct it as the proper voltage and frequency using pulse with modulation. That's going to be a fairly expensive thing compared to just connecting some wires across mains. Even changing voltage is using a transformer means that you're going to need transformer capable of potentially converting multiple kilowatts of power, and that's not an inexpensive touch either.

Are you going to pay for a feature you'll never use?

Engineering for 220v/50hz requires completely different wiring and componentry than for 110v/60hz.

Also, it's not "region locked" - these are truly incompatible electrical systems.

It costs more to make things multi-voltage. For small electronics that run off DC, it turns out that the 'costs more' for having an auto-switching power brick is less than the 'costs more' of dealing with stocking multiple different power supplies to be sold to different regions.

With higher-power appliances that don't just run off DC, where you actually need the thing itself to be different, it turns out that having multiple variants (or only selling to one region) is cheaper.

Toasters are a great example because you're pretty much just shorting a wire into the plug, but it's a wire whose resistance is very carefully chosen so that it gets hot but doesn't burn up for the voltage of the grid it's being plugged into. To make something like that multi-voltage you would need multiple paths for the power to flow and some sort of ability to switch things, all of which costs more money than not having that.

Of course, that's all 'in general'. It's always going to come down to the specific factors related whatever the thing is, who's making it and who it's trying to be sold to.

The wrong frequency in itself is bad for transformers, then some motors wouldn't run at the correct speed

Edit: the Japanese grid is fantastic in that regard

(looks at rule 2.)