Italians tend to gravitate towards "known best" brands. It's both regional, and family-based. Some families may buy only Illy coffe, but most romans buy Lavazza, specifically Qualita' Rossa. Barilla, Buitoni and DeCecco dominate the pasta market, despite hundreds of smaller brands existing. From naples downwards, Voiello is the go-to brand.
Berio is THE olive oil almost everywhere. This does not mean that it's better; my dad lived in a small village in tuscany and he would go to "a guy" and buy actual real farm-made olive oil and i gotta tell you, there is no comparison.
But these brands are reliable, good value for money, of respectable quality, and as such they dominate. And when you are a shopkeeper and Berio is the one brand that outsells all others at several times over, you just don't stock the losing brands anymore.
There are historical reasons why as well. Both the shift in industrial production in the postwar era, which led to some companies being far more successful than others, and also the advent of tv commercials.
Back then we italians had initially one, and then two TV channels. Rai 3 was the third and got added in 1979. Rete 4 (Mediaset, Berlusconi) came in 1982.
Between 1957 and 1977 we had the singularly most popular TV show ever in italy which was Carosello, whose formula was a brief comedy sketch, then an ad. Book one of those ads and your product will outsell all competitors.
Early TV ads were ridiculously successful, and brands which managed to get a tv spot would crush the competition. Food brands that were advertised in the 50s are still active and dominating today.
Mind you, it's good stuff. It's easy to make good stuff in italy, with the climate they got. But the only way into the mass market today is either through discount branding, or niche placement. You can't start a pasta, olive oil, etc factory and expect to compete.