TL;DR Decisions made long before the global trade in electrical appliances was thought of.
The UK started out with DC which ranged from 110 to 250 volts, this was generated by independent electricity companies and had a very limited distribution range because it was inefficient to distribute over long distances.
It gradually changed over to AC with about the same voltage range and a frequency range of 40 to 100 Hz depending on where you lived. Eventually 240v AC @ 50Hz was adopted as the standard. The USA probably had a similar evolutionary process but with a different outcome.
The EU had several different voltages, all around 230v, that were harmonised in the 1990's. I say harmonised but it was a just a fudge, what happened was the different countries continued using the same voltage but the tolerance was increased so all countries fell within it.