That's an interesting question.
The general picture in the 90s, with football globalization, was: clubs were piss poor in Brazil, no structure, so they had to produce players to sell in large scale. That's why there's always been great investment in youth. Also, with so many players leaving, there was a lot of room for youngsters who did well in youth.
With that space, there wasn't the need to have a B side or even to loan out all the kids. Traditionally, if the kid is really good, u let him practice with professionals for a while and inserts him little by little in non important games. This is considered the best way to develop a youngster here. Only the average ones are loaned out to gather experience. Or the ones who don't fit in well in the professional squad. But if the kid shows potential, you actually trust him and give him a bigger role, little by little. Loaning out is almost a plan B, if the kid doesn't do well as a professional, or if you are dealing with average material.
Here, almost all big clubs have their squad composed of 1/4 or 1/3 of players who came from youth rankings. Even if their job is basically to fill in the squad and play occasionaly. If the kid is used to deal with the pressure of playing in a big club from the beginning, even if playing a small part, this is considered a better experience than being an important player for a small club.
However, many kids can be thrown at the fire if the team is doing really bad and they have to step in and solve out the problem. But the good ones will never complain about lack of opportunities.
PS: it was the need to sell that actually screwed Brazilian football. In the 90s and 2000s, clubs actually selected youngsters to play in their youth ranks according to what was needed in Europe: strong and athletic players, leaving skillful small players aside. That's why the quality over here dropped a lot. Now it's starting to get better again, as Europe is now prioritizing skill instead of size, even in highly competitive leagues as Serie A. Also, now there's less space for youngsters, because clubs have money and are structured. Brazilian league developed a lot with the country's economic growth and clubs are able to keep their top players. Anyway, youngsters still have a lot of space in here and clubs invest a lot on them. And actually trust them. It's a cultural matter.
For instance, kids as Neymar, Oscar, Lucas, Ronaldo, Romario, Ronaldinho, Kaka, etc, were NEVER loaned. This wasn't even considered. If you have a gem or a very promising player, you keep him and let him learn with the best. And more importantly, you give him a bigger role as he plays well.
I think in Italy they just don't trust youngsters enough. So they lack transition, as a B side. Actually, this is changing. Due to hard times, clubs are obliged to invest in youth because it's cheaper. I think Italy will start (actually has already started) producing more and more youngsters. And actually in a few years I believe there will be B sides.