The box office numbers actually being offered by the studio to the public when ST:TMP finished its first run in 1980 put the take at 56 million domestic. I have no idea how the higher numbers that have been published in more recent years were derived.
People in the U.S. "didn't keep going in droves" to see this movie - it was hard to get in on the first week, but the big venues (like the MacArthur, where it had its world premiere) were not selling out shows by the second, and within six weeks you had to hunt for the movie in a metropolitan area like Washington, DC. Many cinema owners were frustrated with it because it did its best business early (in those days, at least, the studio and distributors took a huge chunk of first week's box office, with the exhibitors receiving a greater percentage as each week passed - hence the enthusiasm of theater owners for movies like Star Wars, which had great legs. Trek did not). Not only did critics fairly dismiss the movie but word-of-mouth was not good. It was not Star Wars, Close Encounters or even Superman.
The non-fans I saw it with were unimpressed ("this is what trekkies have been fussing about all these years?"), and most of the Trek fans I knew were disappointed.