Bulb and co are largely only sellers not generators. I don't see that this needs to be nationalised but plainly some degree of risk management improvement is required because these failed firms lacked the financial resources to ride through and respond to market fluctuations which is plainly a failure of regulation.
With regard to the bail out, I don't think the Government could allow the firm to cease operating in the same manner as the previous firms. The big players were already saturated with new customers following earlier failures and 1.7m customers was just too much to expect them to absord. It is a reasonable if undesireable reaction.
Now the risk associated with energy generation is substatial and growing and there is no market really because every single player is subject to explicit or implicit subsidies from the state or bill payer. In this "market" we are seeing no security of supply investment without subsidy and then only in useless things like gas engines. Natioanlisation might actually be a rational way to see us through the energy transition because I fear the technical risks are growing with no remedial action in sight.