It comes down to the cost of changing. All these systems were independently developed as electricity become standard in homes. In the UK for example, the standard was developed in 1947 - electricity was already in the country but there wasn’t national standardisation in infrastructure, so when that happened a standard plug was introduced. And this was also done in other commonwealth countries including Ireland (which is very integrated with the UK grid), Australia, New Zealand and others. They are so embedded in each country that it’s near impossible to change them all - or when it is possible (e.g. the UK & Ireland could change to an EU standard gradually) it’s just not deemed worth the cost - the old standard would need to be maintained for a long time, and at some point people would need to be forced to change to get it done.

There was never a successful global effort standardise plugs. Globalisation wasn’t really a thing in those days so there wasn’t enough support for pushes for global standards. There was a lot of regional standardisation though - large parts of Europe have the same electricty supply and separately North American between Canada and the USA, due to the pragmatic issue of sharing grids. 8 Plugs when there are over 100 countries isn’t terrible.

“Region” locking now is basically 3 types. Some devices don’t have transformers, so those devices - like kettles - are designed to directly use the local electricity supply. Those are very much more “region locked”, but not necessarily to 1 plug; for example in Europe while the plugs are different the actual grid is pretty similar.

Many devices do need transformers - like modern Laptops / TVs / Mobile phones etc - the local supply is converted from high voltage to low voltage. Most of those transformers are external or can even be built into the plug, while others are built into the device. That means items can be sold to multiple areas with just the external power supply being different. When the transformer is built in that does “region lock” the products. An ATX desktop PC for example has a Power Supply Unit which is regional; but all the components are international and inter changable. Meanwhile a small form desktop these days has an external transformer much like a laptop and is much less region locked.

And now of course, USB has become a defacto standard to the point that many new devices don’t come with their own chargers and rely on whatever the customer has. And increasingly USB outlets are being added to public spaces across the globe, and people can change their own plugs to include a regional socket and USB outlets.

USB is probably going to be the defacto consumer facing charging for many uses, alongside the regional plugs for devices where USB doesn’t make sense. But the background grid differences between say North America and Europe is unlikely to ever change, due to the massive cost of changing the entire grid.