The CRJ is essentially a lengthened Challenger business jet. The reason that the CRJ is not designated a CL-600 like it's counterpart is due to the airlines. At one time, the CRJ had the same designation and many pilots were using the airlines to get free training essentially. They would get typed and then jump over into a corporate job flying the Challenger. This was costing the airlines money, so they went to the FAA and got the type certificate changed to a CL-65. So now it requires two different type ratings.