Why might an "inequitable conduct" defense to patent infringement be a more attractive defense than an "invalidity" defense?

If a single claim of a patent is found to be invalid, the remaining claims of the patent can still survive if they do not suffer the same defect.  See 35 U.S.C. 288.  By stark contrast, if inequitable conduct is proven, the entire patent will be held unenforceable. Bristol-Myers Squibb Co. v. Rone-Poulenc Rorer, Inc., 326 F.3d 1226, 1233 (Fed. Cir. 2003).  Note that my question may make it seem like the defendant must choose a single defensive theory to run with at trial. In actual practice, however, defendants frequently raise both invalidity and inequitable conduct defenses (and sometimes even other defenses as well).