Because black is still in check.
Why Canchu En Passant Outta Check ?

ok. white just played Qb5+
now...if i play 1...c5 then white has the option to play 2. pxp e.p. and the game continues.

My guess is that the white pawn on the d file doesn't have to accept the en passant. The white queen could just dip down to the 8th rank on the next move and have the king in check again.

ok. white just played Qb5+
now...if i play 1...c5 then white has the option to play 2. pxp e.p. and the game continues.
1...c5 is an illegal move. Black is still in check.

My guess is that the white pawn on the d file doesn't have to accept the en passant. The white queen could just dip down to the 8th rank on the next move and have the king in check again.
but FIDE rules assume NOTHING...thats their hallmark !

ok. white just played Qb5+
now...if i play 1...c5 then white has the option to play 2. pxp e.p. and the game continues.
1...c5 is an illegal move. Black is still in check.
and thats my argument !...it can become a legal move 'depending' on white's choice to proceed !

I just noticed that @KetoOn1963. The king would still be in check. the move c5 by white in that circumstance would be an illegal move.

you see ?....if i played 1...c6 then the game continues without any questions about legality, right ?

That is true. If you played c6 then white would play Qxc6+.
but that cant be assumed ! white may take with pawn.

ok. white just played Qb5+
now...if i play 1...c5 then white has the option to play 2. pxp e.p. and the game continues.
1...c5 is an illegal move. Black is still in check.
and thats my argument !...it can become a legal move 'depending' on white's choice to proceed !
With that logic, checkmate doesn't exist. I can put my king in check, because my opponent might not capture my king.
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