who thought that "small" meant "cheap" and that's what they produced, the rolling bomb called the Pinto and the car famous for rusting on the showroom floor, the Vega (which also featured engines that self destructed). The cars were badly made, tinny, and no damned fun to drive since they ignored basic ergonomics. They slit their own throats that way and are only now starting to produce the high quality, fuel saving small cars they should have done from the start. They still don't advertise them as heavily they do the big gas guzzling SUVs and trucks.
The truth is that VW had already made inroads, offering fuel efficient small cars since the 1950s. Toyota just picked up another share of the market for small cars, especially in urban areas. There was a big market for them that the Big Three missed entirely, and that market existed long before OPEC did.
Management greed also helped kill off the industry, greed that got around the unions by outsourcing parts manufacture--first to the south and then outside the borders. Only the final assembly remained in Michigan, and even that was under fire from greedheads in the carpeted offices. Yes, their advertising budgets were higher than wages. However, advertising revenue is seen as having money roll in, while the people actually doing the work of making the product were always seen as money rolling out. This is a POV that exists in management courses country wide and is responsible for most of the ills today as workers are devalued completely.
Flint used to be the American Dream, good jobs allowing workers to own their own homes and buy the products they spent their lives making. The main problem is that it was reliant on only one industry, so it was easy to kill when that industry's executives managed to foul everything others had built up completely.
NAFTA and GATT were just final nails in the coffin that had been built by bad management that had misread the market, been too slow to modernize and mechanize manufacturing, and allowed inferior products to roll off the line, expecting advertising to sell them to a public that really wanted to buy American, but got turned off fast.