1. More number of core developers and open research: With more developers involved, every proposal is carefully considered and debated, ensuring that the best decisions are made for the long-term health of the network.
2. 9 clients’ implementation: The network update had to be coordinated across all 9 clients, which added to the time needed for the update.
3. Extensive testing: The Beacon Chain was shipped on December 1, 2020, and the mainnet was moved to proof of stake on September 15, 2022. This was a period of 21 months of extensive testing to ensure the stability and security of the network.
4. Simplify the protocol: The initial proof of stake implementation was complex, so the team decided to start over and build a simpler, more robust network.
5. Backward compatibility: The protocol update had to be designed in a way that would not break existing smart contracts and would be backward compatible.
6. The network never went down: Throughout the update process, the Ethereum network remained online and accessible, with no downtime or disruptions.

Overall, the long development process was necessary to ensure the stability and security of the Ethereum network. The team’s commitment to building a robust and reliable protocol is a testament to their focus on the “infinite game” of building a sustainable blockchain ecosystem.