When they both come out, around 1990s, there was no CL coupe. Check this:
http://en.wikipedia.org/wiki/BMW_8_Series
The 8 series did not sell very well, where as the SL went on to become a very profitable class/series for MB.
Also, despite the V12, the 850i was actually underpowered compare to MB 500SL at the time (V8).
Anyways, it was a good looking car, just never took off in terms of sales. I am sure it's a big disappointment for BMW because they spend a lot of money developing it.