Steve, when it comes to new releases I can't find the logic. Amy Helm's older album was offered on both LP and CD, the newer one on CD only.
When it comes to reissues, the great reissue labels (MoFi---don't listen to those who have heard only the pre-Music Direct ownership releases, Analogue Productions, Speakers Corner, Intervention, Light In The Attic, all the Jazz-focus labels), they sign deals to get access to the master tapes, deals which stipulate either a certain length of time they may produce LP's, and/or number of LP's they may manufacture, and sometimes the playing speed (such as 45RPM only, when the major label wants to market their own 33-1/3 LP of a given title).
If the growth of new LP sales continues to grow, watch the major labels get tighter with their licensing agreements. Buy 'em while you can, boys!