In the case of I2P, the project has over 20 years of active development. The transports and network have proven success at creating access within the network for people facing restrictions to their communication.
What it needs is not to make anything new, it needs maintainers.
In my 8 years and counting of participating in research, development and outreach, I can tell you that each of us in the core team are doing a whole departments worth of work.