It’s because, like many things, power sockets were all developed individually by countries back in the early-to-mid 20th Century. So you end up with loads of incompatible local standards.
Now there is some crossover. For example, countries like Malaysia and Singapore use the British BS 1363 “Type G” plug, whilst counties like Japan and the Philippines, which have a strong US influence, use the US IEC 60906-2 “Type A” plugs.
Also, within Europe, many countries, including Italy, use the Europlug “Type C” which is broadly compatible with a range of other sockets commonly used in Europe, including the French CEE 7/5 “Type E” and the German CEE 7/3 “Type F”.
However, the Type C is neither polarised (you can insert it any way around), nor grounded which makes it unsuitable for many devices. So, given a lack of any standard, many countries have come up with their own versions which include either a polarisation key, a ground connection, or both. And, guess what, they are all different!
The Italian version of this is the CEI 23-50 “Type L”. Interestingly (or not), the Italians have two power sockets which are incompatible with each other, deliberately! The original reason for this is because one was for lighting and the other for non-lighting, and they were metered at different rates and taxed differently. Nowadays they are designated as 10A and 16A. The CEI 23-50 10A sockets are compatible with “Type C” Europlugs.
There’s nothing fundamentally wrong with the Italian Type L other than it’s different from other standards. Having the earth pin between the two live pins seems like a fairly smart design to me.
Aren’t you glad you asked?
Cheers,
Keith
(who has spent far to much of his life dealing with plugs and sockets)
… although in the north they are less and less common those weird things 
…
