Well, it was refurbished as a result of the Union Station Redevelopment Act of 1981, a public-private endeavor signed by Ronald Reagan.
I remember using Union Station in the 70's. It was terrible. Carter had managed some kind of bicentennial development effort, outfitting the Main Hall with a recessed pit to display a slide show presentation. This was officially the PAVE (Primary Audio-Visual Experience), but was sarcastically referred to by us who used the station as "the Pit."
That redevelopment act was a loooooong time in coming. A client at the firm where I worked in the mid- to late- 60’s was involved then in Union Station refurbishing and redevelopment, lobbying PR, raising $$, etc. Interestingly, he’d made his $$$ in the early days of the airlines.