Prof Pixel has this completely right.
Land had dreamed of Instant color movies as soon as he got the Model 95 on the shelves at Jordan Marsh. However, all efforts to get a working subtractive color transparency film failed. Land's determination and focus of attention that made him famous were his undoing when it came to Polavision.
Land didn't take the introduction of the first bulky, expensive portable color video systems as a warning to scrap the additive reseau color system, he took it as a reason to put the dull, unsharp, 15" picture on the market immediately. Truth be known, a Polavision kit was a lot less expensive than a 1978 home video system, and the Polavision camera far more portable than the video equipment, but the Polavision image was too compromised, and it was obvious that video would become cheaper and more portable quickly.
I even wonder if Polavision was Polaroid 's undoing. It was a colossal marketplace failure, and a very large investment had been made to bring it to market. After Polavision, their successful instant color print products were being priced at a dollar per shot. They probably did that to recoup some of the losses incurred in the Polavision debacle, but dollar-a-shot probably got people to go back to conventional still cameras, starving Polaroid of cash.