Large projects tend to end up under the various foundations because large projects have lots of common problems that the foundations help solve and it doesn't make sense to reinvent the wheel every time (e.g. by starting your own foundation).

Once there, lots of stakeholders are more comfortable committing lots of resources because the governance rules are predictable and well understood. So the projects tend to cater to those stakeholders, putting a higher emphasis on backwards compatibility and evolving more through extension than through revolutionary, breaking changes.

Projects which go to foundations live for a long time. And they don't stop innovating, either -- they just innovate more at the edges than at the core.