They only made Plymouth Superbirds for one year for that same reason.
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Superbirds were made for one year and Daytonas were made for one year ,, they were no different than any other RoadRunner except for the aerodynamic aids. They were not made after that limited run because they had served their homologation purpose (qualified as production so they could be raced in NASCAR events)... that’s all.
Even with very limited production many remained on dealer lots unsold , some until 1973.. They were highly impractical and easily damaged. If you had bought one in 1973 for about $3,000 and garaged it you could buy a nice house with acreage for what it would bring now.
I do know of a guy in Va Beach who bought two brand new. One with the 440 six pack, the other with the Hemi. Garaged them both and only takes them out on the prettiest Sunday afternoons. Both still have under 10,000 miles. He knew exactly hiw they were going to appreciate and what he’s sitting on.