Because long ago it was "she singeth" (I don't know why) and "she sings" sounds like that.
lala sings it prima j sings homegirls/
who sings that thing you do???
Urbandub sings it.
who sings bacon
Avril Lavigne sings this
noone sings that
Rey Mysterio sings it.
Twista sings wetter
Joe sings himself.
Usher sings omg
Ryan miller sings it
I Sings was created in 1999.