I've had those experiences, but I've also had the opposite experience. I used to work for a regional internet service provider/cable/phone company that was owned by PE. They poured a ton of resources into the business, improved our processes and standardized things so that we could expand to more regions.
Then they sold us for a nice chunk of money (for themselves, but employees got better pay and benefits under the new company). The new parent used our practices as the model to use across the whole business.
It was a good deal.