Actually, it’s not just grinder time but also the delivery time.

“Most” billet roller cams start as semi-finished cores.
They have a lobe lift, lsa, and duration in that configuration.

The bearing journals are done, along with the dist gear being cut........ and, the heat treat is already done.
The heat treat on a billet core doesn’t go all that deep(deeper on some material than others), so the finished product can’t be way off than what the semi finished core starts out as.

To do a cam from an UGL core, which is not heat treated, you burn up 2 roughing wheels(about $100/ea) getting the profile semi roughed in on the core.

Then it needs to be sent out for heat treating....... which is where the big time delay occurs.
After getting it back from heat treating it gets the cam lobes finished.

It’s a much more efficient process to get a cam done from the semi-finished core.