People looked at how the cost of wind and solar went down and made a assumption that green hydrogen would follow. The reasoning was that the cost of green hydrogen was energy, and thus at some point green hydrogen would be too cheap to meter.

The whole energy plan of central/northen Europe, especially Germany, was built for the last several decades on the idea that they would combine wind, solar and cheap natural gas and then replace the natural gas part with green hydrogen. In Sweden there were even several municipalities that spear headed this by switching mass transportation and heating towards hydrogen, initially with hydrogen produced through natural gas, as a way to get ahead on this plan.

The more sensible project were the green steel project. As experts in green hydrogen said consistently said through those decades, is that green steel would be the real test to make green hydrogen economical. The economics of burning it for energy or transportation would come several decades later, if ever. The green steel project however has not ended up as planned and gotten severely delayed and has seen a cost increase by an estimated 10x. municipalities are now giving up the hydrogen infrastructure and giving it an early retirement, as maintenance costs was significantly underestimated. There is very little talk now about replacing natural gas with green hydrogen, and the new plan is instead to replace the natural gas with bio fuels, hinted at carbon capture, at some unspecified time.