Liability insurance, physician backup, hospital privileging, and for some, truly believing that it is too risky and desiring to have help close at hand "just in case". HeartsOpen: no, the state boards do not often restrict where MDs practice, but obviously their medmal insurers do. They'd be dropped like a hot potato or have their rates jacked up sky-high. And obviously the state can't absolutely restrict where birth happens, but they do license health care professionals. So in states where homebirth midwifery is severely restricted or illegal, a mother can definitely give birth at home. She just can't be assisted. This is how state laws are actually leading people to attempt "UCs" when they could be attended by competent professionals, or hiring unlicensed midwives who got their training who-knows-where and are not being held to any standard other than word of mouth.