There are a couple of possible reasons.  If the tree is growing in too much
shade, then it probably won’t flower.  While dogwoods don’t prefer all day
sun, they do need to get 7-9 hours daily to flower as we expect.  Another
issue could be lack of nutrition.  Do you feed your tree.  I’d suggest
pounding some holes in the ground about 1′ deep with a pipe around the tree
out away from the trunk of the tree about as far as the outermost branch
tips.  Fill those holes about 3/4 full with Espoma Bio-tone starter food.
This will provide nutrients but, even more important, a dose of beneficial
microbes and fungi that will enhance the tree ability to absorb phosphorus
from the soil.  Here’s a link to more on that.

http://blog.timesunion.com/gardening/sorry-bone-meal-ive-met-someone-new/6303/

Then, feed it with Espoma Tree-tone in the same manner every spring as soon
as the ground thaws.

Finally, check to make sure that you haven’t been piling mulch up against
the trunk of the tree.  Mulch is good on the soil but not against the bark
of the tree.  The mulch prevents the easy flow of nutrients up through the
bark and is slowly strangling the tree.  Brush any mulch away from the trunk
of the tree until you expose the original soil level.

Peter Bowden