Not a historian, nor Italian, so double check me on this, but a big part of the "why" is that the facists were never removed from Italy. They've just been kind of allowed to fester since 1946. I mean, Germany didn't really get rid of their facists either, but the Italian facist movement was basically unscathed. Movimento Sociale Italiano (MSI) was founded in 1946 by Facists literally from Mussolini's party, and maintained relevance by making political alliances with other, more moderate conservative parties.
Some facists just straight up joined the Liberal parties. Fernando Tambroni, Christian Democratic Prime Minister of Italy for 116 days in 1960, for instance, was a Facist Party member during the war, and was quite the fan of Mussolini. The subsequent Prime Minister, Christian Democrat Party leader, Amintore Fanfani, who served five non-consecutive terms as PM, was also a member of the Facist Party.
In the 90s other facist parties, particularly Forza Italia, and Alleanza Nazionale were spun off from MSI and basically wore a better better mask, and managed to get Berlusconi, also a Mussolini Stan, in as PM.
We could continue doing pointing out facists in powerful positions in Italian politics, and we skipped the whole "decades of facist terrorism" thing, but really the reason Italy jumped to fascism is because it has been there the whole time, and has had power semi-regularly.