You are probably comparing your fairly young plants to more mature trees. It could just be a matter of giving them more time to get established. CMs do bloom better in full sun, and if you planted yours where they get shaded out, that could be a reason as well.

Suja has a point.
You can deadhead them, which on my shrub type, I sometimes do. I clip off the whole cluster. Be careful that you're cutting OLD ones, vs. the new ones, because they look pretty similar.

You didn't talk about the sun exposure. These puppies need a good 7-8 hours a day of sun to bloom well.
Fertilizing should be done in the spring, when things are just warming up.

Christine