Are the flowers true to the cultivar? If so, give it time. Reasons why things like this happen are often not explainable, unless there's something keen to Cornus grafting that I do not know about (selection of graft wood).

Dax

looks to me.. like there are suckers coming from the root stock.. and they all need to be removed below ground...

and then another picture to see what is left ...

your plant was grafted to a standard ... so you might have as many as tree trees there... speculation alert ...

the one with the roots...

the trunk to about 3 to 4 feet..

and then the pretty flower one .... which is the only one you want to leaf and flower ...

get us a pic at the ground.. and we can do more than speculate...

ken

Thanks for the feedback! I didn't realize that this cultivar was grown on root-stock. The suckers appear to be sprouting from the tree trunk just above the flare. I'll post a close-up photo shortly. I cut the suckers each year but they come back with a vengence. I'm debating whether to replace this tree but will keep it if its appearance can be improved. I had one arborist look at it and he just laughed. His suggestion was to cut the central leader to the ground and use it as a shrub.

ON more thing.... to answer gardener365's question:
The flowers look true to the cultivar but are extremely sparce.... alot of vegetative growth but few flowers. The tree grows upwards at a rate of ~1 ft/year.

It's a little young for full flowering. Did you fertilize your lawn?
Not all Kousas are grafted. They self seed fairly readily for me. Named varieties are grafted though. I wouldn't be in too much of a hurry to strip the trunk of the sprouts. The trunk can be susceptible to sunburn if suddenly exposed during the summer. I would remove the lower foot or two of branches though, but no more now. Wait until the crown forms and shades the trunk a bit before removing the rest. That's what I would do and I have a lot of them.
I'd be more worried about the overhead power and telephone lines.