The reason the law exists starts with GM...
I always thought the European manufacturers in conjunction with their US dealership network were the ones who raised the loudest cries. Mercedes was sick of all the 500SL, SEL and SEC's coming in through the grey market. BMW wanted to put a halt to the 323i and 745i imports. Porsche was tired of all the 930's coming in to the US through the grey market. Ferrari had had enough with all the Boxers coming in through the back door. There were even grey market Honda Preludes with efi and alb (their version of abs) years before they were available through the US dealers.
I don't recall any GM products that were high on the list of grey market conversions back in the 1980's.
The 1986 model year was the when everything changed. I owned a 1985 grey market Range Rover. Saw plenty that were older but never saw an actual 1986 model year Range Rover here in the US (that's not to say there wasn't one or two). With the simultaneous crack down in the grey market, most of the European manufacturers began offering bigger engined versions of their vehicles. The 560 engine premiered in 1986 in the SL, SEC and SEL. BMW offered the E32 with a larger engine and in 1987 introduced the V12 and the first M3 to counter the old 323i. Porsche reintroduced the Turbo in 1986.
Meanwhile, 1986 saw the shutdown of may grey market importers. The task for certification for these imports became monumental. About the only importer I can think of that remained was Europa Imports an importer of G-Wagens out in New Mexico. He had some help from Mercedes/Steyr in getting the trucks certified but I think his business is a shadow of what it once was.