What goes wrong in regulated utilities?

For one reason or another I’ve recently been dealing with lots of big companies in markets where new entrants find it difficult because of the way they are regulated. They all have one thing in common — terrible customer service. I’m wondering whether it’s just a coincidence or whether there’s something inherently wrong in the basic way we regulate markets like banking, electricity, broadband, mobile phones, insurance and many more that leads them to have no incentive to improve.