Why Bxc4 gives +2.5?

Why Bxc4 is by far the best move?
I usually retreat with the queen with those kind of positions, but here the Bxc4 is gives +2.5!!! and the rest of the move are only +0.5

This is not bad to lose the bishop pair?

I don't get the +2.5, someone have a clue?

You're right. why do u think that the dark bishop is more valuable here? my pawn structure is still pretty dynamic i guess. black can castle king or queen-side (q-s is better i guess)

I don't think that is a correct explanation.

For one, I don't see why the dark-squared bishop would be inherently better than the light-squared one in this particular position. More importantly, I feel the most crucial feature here is white's development advantage. By playing 1. Bxc4 white avoids having to move his queen second time and instead exchanges his undeveloped bishop to black's active knight gaining further time.

After 1. Bxc4 Bxc4 white simply continues 2. Nf3 and is more or less fully developed whereas black still needs few moves to castle. White can use his development advantage to force further concessions from black before he can finnish his development. Additionally, the black bishop in c4 is somewhat loose and in some variations white may be able to gain further time by attacking it. For example, if black tries to castle short with 2... Be7 then 3. e5! seems to be akward to meet.

Pretty much what says post #4. Black is fatally back in development, and he will drop something while trying to bring the king to safety.