In 'grep' - Why does it behave this way?

In 'grep' - Why does it behave this way?

File still contains:
a
b
c
d
And
grep -v -e "a" -e "d" still
gives:
b
c
which is expected.
Now, file fill contains:
a,b,c,d
My command
grep -v -e "a" -e "d" fill
I expected it to give me ,b,c,. But, I get no output. Why ?