Why does it take CA so long to count votes?

There are still 2 House districts in CA that have not been called. Currently they are both separated by .2% with 97 and 93 % of votes counted. In one race the GOP candidate is ahead, in the other it's the Dem. It's been 2 weeks since election day.
SGT James Murphy, CPT Jack Durish,
SPC Gary Welch, SGT Mark Anderson,
CPL Douglas Chrysler, LTC Trent Klug,
CSM Charles Hayden, SMSgt David A Asbury,
SSG William Jones,LTC David Brown
SSG Michael Noll, MAJ Dale E. Wilson, Ph.D.
SGM Erik Marquez, CW3 Harvey K.
SFC William Farrell, CPL Ronald Keyes Jr
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