Why would it take 50 years to install signalling across the system ? Caltrain is on year 5 of their "3 year" project to modernize their signaling system... and

Why would it take 50 years to install signalling across the system ? Caltrain is on year 5 of their "3 year" project to modernize their signaling system... and that's a relatively simple 75 mile system with 30 stations and it's almost all above-ground.