Good questions, let's wait for the good players to speak...
In the meantime, I suppose the Spanish has more subtleties and complications than the Italian so the good player can think 'If you can't handle it, you'll lose'. That might not be the case with the Italian-you could get away with ploppy moves.
As for2.f4 in the Sicilian, I was just contemplating the same thing myself...
1.why ruy is better than italian
The Lopez is considered better because it sets more problems over a longer time period for Black to solve than than Italian game. This basically means that White has better chances to win since Black has more opportunities to end up in a position where Black can make more errors.
2.why 2.f4 is not good in sicilian
2. f4 is not so great since Black can equalize faster with 2. ... d5. Some players will play 1. e4 c5 2. Nc3 followed by 3. f4 to stop d5 for awhile and get nearly the same positions as from 2. f4.
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