Forcing all costs on to new entrants in a market is generally a bad thing for the market and causes it to not expand fast enough. Also they may just choose to not participate in the market at all. I.e they'll bring in a whole lot of natural gas generators, put them in the parking lot and call it good, which is not a good thing long term.

Why would any reasonable governing entity (I understand we live in a world where there are not many of these) allow you to run a bunch of natural gas generators in a parking lot?

Forcing all costs into externalities is also not ideal. Right now, some state's systems, force residential consumers to pay for new infrastructure for new demand while only minimal costs are paid by the new customer.