Caro-Kann - Advance Variation (3...c5) question

Hello. Could anybody explain why the move 4... Bf5 is so rare in the situation given below:

Personally, I'd be tempted to play it in order to free my bishop before making an usual e6 move.

It's one of the main-ideas of 3...c5, to be much more flexible with the development of the Bc8. If you want to place your Bishop outside the pawn-chain, on f5, than you can play 3...Bf5 followed by e6. After 3...c5 you wait with the bishop-development, because in some lines the best square is g4, and sometimes it's also ok to lock the bishop in (for example after 4.dc e6, Black want to play a French Advance, with White commited to the premature dc-move)

The only variation after 3...c5, in which Black develops his bishop to f5 to my knowledge, is 3...c5 4.c3 Nc6 5.Be2 (Patzers usually play 5.Nf3) and now Black has no choice: 5...Bf5 transposing to one of the mainlines of the Short-System.

the most obvious reason i can see is that it threatens nothing and black is already behind.i have no idea what  the theory is  here but i would probably play Nc6.it feels better than Bf5,sorry if my explanation is poor..or i could say that Bf5 feels like too much of a luxury in the given position and bad things can happen to black if he does not develop quickly and accurately.after all he is playing a kind of french a tempo down.in my patzer opinion ..3Bf5 is the way to go.

I think the following position might be part of the reason?

At least as far as I can see, in this position, black's development will be very slow while white has many options. The pin on the knight with the center spacial advantage should be enough to get a long lasting advantage with white against an equally rated player.

This is like an anti-gambit, you lose a pawn and your development gets slowed to a crawl. 

3. ... c5 is the 2nd-most common move.