To clarify, they had already been suspended for the pandemic schedule. They were weekday only supplements that gave passengers a one-seat ride into downtown.
I'm not sure if they will disappear completely, or whether like the J-Line, amaze people by turning up in special circumstances (Florida Station <> Union Station).
Here are passengers in a 2013 baseball crowd at Union Station being surprised by a C-Line extra after the day's normal shutdown time.
The alternative southbound is timed transfers at I-25 & Broadway, The D-Line to Mineral is on the right and the E-Line to Lone Tree is on the left.
The alternatives northbound are a 3-minute or 6-minute wait for the transfer at I-25 & Broadway.
Motivation for the change is the continued low occupancy of downtown offices and a decline in college attendance. The long-term plan calls for the headways on the remaining lines to be improved when traffic increases, which sounds reasonable. It actually would cause chaos unless it is done on all of the overlapping lines (D, E, H, W) at the same time and if downtown traffic signals are retimed. However, that will not be an issue until the consultants are safely out of town.