Why is the tow capicity (2000 pounds) so low in a rear drive big V-6?
Because the SRX is based on the CTS (saloon). Therefore, it is not optimised for towing.
My 07 with Utility Package has a tow rating of 4250 lbs. But the max on the 08 models is 3500 lbs.
The frame obviously won't support a higher tow weight. Trade it and buy something more suitable for you needs.