They were introduced and installed and became common and at some point declared regional standards at the time when there were no standards at all. You’d visit your local shop and buy your four lamps in your entire lifetime with a plug that fits the socket and you’d be happy that you have this new electricity thing in your house. There would be no reason for anybody to be interested in what the sockets and the plugs look like in the neighbouring country, not to mention some far away land.