It's a multi year programme.. to competr at the top end we need to consistently be in the CL, we need to get new sponsorship deals from it, we need the Italian league as a whole to massively step up their game... a large number of things.
The biggest chance for this was Italy to bid for the 2024 Euro. Imo they'd win it, but obviously one cannot know that. Germany hosted a World Cup 12 years ago, Italy's last tournament was 28 years ago. Now the 2028 tournament is too far away to force the state to make some moves about stadiums. The 2030 World Cup is also too far away.
There is only one reason why Italy didn't go for it and a bunch of plausible excuses to go with it. The reason is that FIGC simply does not want this. Why? Because the status quo suits them just fine. Juventus is at the top, being the only club with a new stadium and they don't like the possibility of others following suit. They discover 'scandals' everywhere about other teams because in Italy there's already an obstacle to begin with and you have to go sideways to get what you deserve, which technically speaking is 'breaking the law'. But the law is broken as a whole anyway.
As for excuses? Too many.
1) Italian economy. It's easy to say things like "people are starving and we're throwing away money for stadiums and 1 month long tournaments 6 years from now". Reality is, it will add jobs, construction jobs for the stadiums and a general increase of jobs in the stadium surrounding areas. And it will also bring a long term flow of revenue through an elevated Serie A through tv money and even tourism as a by product.
2) Teams don't have money to build stadiums and the state is not willing to do it. Well, this can be argued, but you only need several venues of 30k or 40k + and teams are actually willing to build stadiums if they come to agreement with the council adn the government. Money is not the biggest issue for clubs, self-financing may be, but money on its own is not the issue.
3) There's the excuse that this is a general waste of money. This isn't the Olympics though where 3/4 of the stadiums aren't used domestically because those sports aren't popular enough. This is football and football still sells. And Italy needs new stadiums.
You usually need 9-10 stadiums. An Italian bid could have the following: A renovated (possibly club owned, hopefully Inter) San Siro to host the final, being over 65k in capacity, Juventus Stadium (40k), Roma's new stadium (50k+), Napoli's new or renovated stadium (35-40k+), Fiorentina's new or renovated stadium (30k+), a possible renovation at the Marassi in Genova (35k+), while the south could be represented through a renovated or new stadium in two of Palermo, Messina, Reggio Calabria or Bari. Bari has both the San Nicola and the della Vittoria that could be renovated or rebuilt for this purpose. The current sad state of the club doesn't mean much, they even had like 20k on average in Serie A. A new or renovated stadium in Verona (30-35k) would also be important geographically. And you would possibly have a second stadium in both Roma and Milano if you need a filler, while there's also Udinese's stadium, a potential new or renovated stadium in Bologna and the Del Mare of Lecce is a nice spot that also needs renovation.
Yes, Germany may look better at the moment or even as a potential host and have larger stadiums, but these things don't go to the objectively best case. And even if the bid failed, it would at least show that the FIGC and the Italian government aren't so corrupt and "backwards" when it comes to this.