@julieca
So either wikipedia is wrong and it only took a year to develop. Or it wasn't William's idea and he came on board a year after development.
I quoted the wikipedia link. It is quite clear what it says and ties in with what Smilesy posted
William's idea in 2018 leading to ongoing research
Earthshot announced 31 December 2019 with a 2020 further date and prizes to be awarded 2021 to 2030
The BBC website reported at the time that more than 60 experts and organisations were involved in the development of the project
The Guardian reported at it's launch in 202
"The prize is supported by a global alliance of partnerships, including WWF and Greenpeace, and there are plans for it to have its own foundation by next year. Backers include the Aga Khan Development Network, Bloomberg Philanthropies, DP World in partnership with Dubai Expo 2020, and the Jack Ma Foundation.
The prizes will be awarded by a council, a global team of high-profile leaders from the environmental, philanthropic, business, sporting and entertainment worlds. The 13 members include actor Cate Blanchett, singer Shakira, Queen Rania of Jordan, Japanese former astronaut Naoko Yamazaki, Brazilian footballer Dani Alves, basketball star Yao Ming and Attenborough."
It takes time to garner such support and representation, hence taking 2 to 3 years to get to the stage of announcing the prizes and initial timeframe. Nobody is saying William did all that himself but given it started out under the umbrella of the Royal Foundation, he clearly has been heavily involved in it.