I highly recommend reading "I'm Glad My Mom Died" by Jennette McCurdy, and watching the "Quiet on Set: The Dark Side of Kids TV" Docu-series. It really helped me understand the mentality of parents like this and what they personally want out of it. "Reliving their youth vicariously" is a pretty good summary, along with the belief that making their kids famous will guarantee them a bright future.
But it absolutely exposes children to exploitation and abuse, and sometimes the abuse can be quite extreme.