Homes were electrified for lighting. So, originally, there were no appliances, only light bulbs, and the only sockets were light bulb sockets. When electric appliances started being made, they were plugged into light sockets. Not convenient, and manufacturers started making sockets and plugs specifically for appliances. But there were no standards - different appliance manufacturers made different incompatible sockets and plugs. This wasn't an accident - the plan was to encourage consumers to continue buying their products, rather than those of competitors, to avoid the inconvenience of changing sockets.
When countries started to standardise, to pick standard socket and plug types, there was already a plethora of types in use. Often, the type that was most common in the country was chosen, which led to the diversity you note. Where standardisation was at the state/province level, standards could and did vary within countries.
This question has been asked before, and the above is just a quick summary of past answers. For more, see:
u/Mitheral in https://www.reddit.com/r/AskHistorians/comments/5gppo2/in_the_us_when_was_the_standard_two_prong/
Fred E. H. Schroeder. (1986). More "Small Things Forgotten": Domestic Electrical Plugs and Receptacles, 1881-1931. Technology and Culture, 27(3), 525-543. doi:10.2307/3105384