Here is a lot of false statements.

Proceed in order.

Whats the different between Sicily and Sardinia ?

In 1861 Sicily was finaly affiliated with Italy. From the end of rome they where under foreign ownership.
After 1861, the state was completely in northern hands. The mafia was the cradle of foreign rule and feudalism.

What was the situation in Sardinia?
Sardinia was affiliated with Spain-Habsburg. Catalan and Sardinian language are connected with each other.
After 1794 sardinia was part for the Kingdome of Sardinia and Piemont. They were never in such extreme way isolated like siciliy.

Organized Crime in Sardinia

In 60's 70's and less in 80's some villages were famous for kidnapping and other stuff.
Sometimes they was called Anonima sequestri. This phenomenon was directly linked to the poverty of the Sardinians.
In Germany sometimes they call guys for jobs for example to burn a house down.This guys were more freelancer i think.

Current situation.

Of course they exist a local organzed crime

For example Old thugs like Graziano Mesina https://www.telegraph.co.uk/news/worldnews/europe/italy/10113587/Sardinian-bandit-hero-returns-to-his-criminal-ways.html

Or new

I'm sure other groups are also in Sardinia. But you have to get local guys are share. The Upperworld ist much more import in Sardinia.

To Malta, the whole island is a single mafia. Cosa nostra can do business. But they don't control the Maltese.
Historical, maltese criminals are strong involved in different racketeering in London. But there are still supposed to be boys from them today