Just over 200 people had RSVP'd for Franks' event on Facebook as of Thursday afternoon.
The photos from the dedication featured more than a dozen people, including Republican Governor Mike Parson and US Senators Claire McCaskill, a Democrat, and Roy Blunt, a Republican.
The Gateway Arch Park Foundation apologised in a statement on Wednesday.
"As organisers of the event, we acknowledge that our ribbon cutting did not reflect the diversity of our community."
A foundation spokeswoman did not immediately respond to a question of whether any black leaders had been invited.
The city is almost 48 per cent black, according to data from the US Census, larger than any other racial group.
The park was dedicated on Tuesday, the culmination of a five-year, US$380 million ($560m) renovation that Missouri political leaders see as a template for the future of the national park system.
It was the first major renovation since the Arch opened in 1965, and about two-thirds of the funding came from private donations.
The 630-foot-tall (192-metre-tall) Arch is a monument to westward expansion that sits along the Mississippi River in downtown St Louis.
- AP