Sicilian Kan pawn break

The opening explorer showed that black won more games playing 9...d6 over 9...d5. Why is this? My guess is that white is better developed and 9...d5 opens lines making black more vulnerable to attacks. If that's so, then would d5 have been better than d6 if I have developed my bishop and castled already? Also on move 10 after 10.exd the computer recommended that I recapture with either the knight or the bishop. My thinking is that capturing with the e pawn would be better because it leaves a pawn in the center and controlling the center with a pawn is good. What conditions would make the pawn recapture better? 

Position after 9. ... d5 10 pxp nxp 11 nxn bxn looks kind of miserable.  White has all sorts of nice options including the surprising 12. c4 (play it out).  White has massively better pieces and development, the two bishops in the open, and may solve the cpawn weakness in some variations.  

I know its said that black usually solves his problems in the sicicillian when he can achieve d5, but the position must always be considered.   

Your pxp is dismissable because you are left with an already blockaded isolated pawn that hems in your bishop.  You can't break the blockade.  White has multiple ways to win -- exploit the lead in development, or trade pieces to a winning endgame where the isolated pawn may be enough of a weakness to win.  

An isolated pawn like this, called an isolani, is only worth it if its central control gives you a dynamic position.  Often where the knight outpost (here ne5) gives an attack.  Here, black's development is probably too bad to achieve it on helpful terms

I thin you are right in that white being ahead in development (which incidentally is typical of many open Sicilians where black often has to be bit defensive during the opening) is the basic reason why d5 is not good in that position.  It can be more viable option when black has castled and is better developped in general but each position must be evaluated individually. The d5-break is not such an automatic way to happiness in Sicilian as one could think.

10... exd5 leads to a really bad version of an isolated d-pawn position (something like 11. Re1 Be7 12. Nf5 and black seems to be in a lot of trouble). Generally the player with an isolani wants to use the active piece play to compensate the static weakness and therefore should not be behind in development. Usually the black player with an isolated d-pawn would want a piece setup like Nc6 + Bd6 + 0-0 + Re8 etc. Here the d-pawn also blocks the diagonal of the bishop in b7 and b5 is wasted move or even weakening. 10... Nxd5 at least leaves black with healthy pawn structure and open diagonal for the bishop even if the problems of the backwards development remain.

According to my experience there are just as many positions in Sicilian where d5 can be played but isn't good than those were it works. Problems may arise because white is better prepared for the opening of the position or because white can answer d5 with e5 when the arising position can easily be a bad version of the French defence for black.