Yes, because the technology is not ready yet. You can't plan a collider if you have no idea how you would have to build it. 20+ years is the time frame for FCC operation, construction could start by 2025. 20+ years is the time frame for planning a plasma acceleration collider, construction would start by 2040 or so if everything works out. Plasma acceleration could lead to higher energies, that leads to things you can study that you cannot study with existing accelerators. The achievable collision rate is unclear.