I believe that the answer is that making a blessing over food is a Birkat
Nehenin, which means that it's a blessing made based on enjoyment. If one
does not derive enjoyment, one need not make such a blessing. (Of course
there are other types of blessings besides the Birkot Nehenin, to which the
rule of the derivation of pleasure does not necessarily apply.)
I hope this helps some!