Because they know it would be a waste of time and energy. DALPA is very good at spooling up their political machine and fending off recall attempts. Combine that with a generally apathetic pilot group, and you would take the focus of the DPA guys off their objective and cause them to waste time and effort on a lost cause. Just take a look at the last major recall attempt a few years ago in ATL if you want to understand what I'm talking about.

Plus, that still doesn't solve the problems with ALPA National and conflict of interest.

I can completely understand why DPA does not consider this to be an alternative.