Yup, the axle has CV joints at both ends. You could take your old one out, replace just the one CV joint that is bad, and reinstall it, but then you have to do all this extra work disassembling the axle, replacing the CV joint, packing it with grease, and reassembling everything. After all that, you still have one old CV joint that will prolly go soon anyway, causing you to have to do the job over again. If you buy a rebuilt axle assembly, you just rip the old axle out, slam the new one in, and toss your old axle in the box, return it, and get your core charge back. It is a lot less of a hassle and you have the benefit of knowing that everything is new. This is what most mechanics do. It is easier for them and better for the customer.