The Supra came about because Toyota wanted to show the world that it had come into its own and was no longer just a cheap imported imitation *cough*
As such it was a demonstration of luxury technology (DOHC, port EFI, 4 wheel disc brakes, cruise control, electronically controlled transmission, etc in 1979). The MK1 was a borderline failure - an afterthought of what they could do by stretching & gussying up a Celica, but the Lotus-engineered MK2 Supra was an absolute hit while still being within reach of most buyers (~$15K MSRP which is equivalent to around ~$45K today)
The MK3 added more cutting edge technology (double wishbone suspension, intercooled turbo, distributorless ignition, etc) but had bloated so much that it was no longer competitive on the track. Its only real saving grace was that it could make monster power. It was also priced out of reach of many ($22,500 MSRP - about $60K in today's money).
The MK4 was Toyota proving that it could beat not just RX7 and 300Zx, but also the Corvette and the rest of the world. It was more of a purist's sports/GT car, but it sold like shit (11,000 some cars total in the US). For $42,000 (~$90,000 today) you could get the enthusiast's choice of a MKIV tt or for the same money you could get the much more comfortable, less ostentatious SC400 with essentially the same chassis. US buyers picked the blander SC400 7 to 1.
The 1990s Japanese asset bubble ("lost decades") had a lot to do with why formerly affordable 300zxtt's and supra and 3000gt and RX7tt's sold so poorly.
For the 2000s-today Toyota no longer had anything to prove. It doesn't need to make a loss-leading sports car to grace the front pages of enthusiast magazines in order to convince everyday Americans that Toyota makes good cars. The average American no longer holds Japanese automakers responsible for Pearl Harbor. Building a MKIV-equivalent would be a money-losing proposition.