"Corporations" are profit-seeking for the entire lifetime; there isn't a point where the making-money comes to the fore and ruins everything.
Automation explains almost all loss of manufacturing jobs. America today manufactures more than it ever has, with very few jobs needed. A car factory today requires a few hundred people, rather than many thousands.
As for why temporary monopoly companies become less innovative, the answer there is somewhat obvious: because innovation isn't the best profit-making strategy. But that's fine: hence the breakdown of temporary monopolies via competition.
Then there's the question of "why china" is where genuine competition comes from, and that's largely due to economies of scale and large pools of talent. The labour costs are secondary for the capacity to automate and integrate supply lines.
America is a massive country with low density, poor infrastructure and limited talent base for relevant skills. The latter is a choice of its citizens to educate themselves in a particular way. The former is the choice of its citizens to vote for particular government programmes: low-density sprawl, and tax-cuts.
If you want to "bring manufacturing back" (whatever that means) you need significant tax raises to build and subsidise significant amounts of infrastructure and subsidise education and training in the relevant skills.
Of course, that isn't as satisfying for a voting for a rable-rouser.