I initially thought this was preventing the "Seely Six" Warner Bros. cartoons from coming to DVD (like the first two seasons of "Quick Draw McGraw," or when Rhino initially planned to release the old Gumby shorts on DVD.) But I believe their theatrical rights are different from the television rights. So far we've had three of them released on DVD ("Hip-Hip Hurry" WAS released on VHS in the 1990s, "Road Runner and Wile E. Coyote's Crash Course"), and I will say the music seemed to work rather well with "Hook, Line and Stinker," compared to the others (ESPECIALLY that crappy "Pre-Hysterical Hare.")
Quite a few of the Capitol Hi-Q music cues, particularly ones composed by Jack Shaindlin and Phil Green, are now part of the APM library, so maybe some of those rights have been transferred.
I remember the "Television's Greatest Hits" album from 1985 re-recorded the "Donna Reed Show" and "Dennis the Menace" themes due to them originally being Capitol Hi-Q music cues (the "Captain Kangaroo" theme, "Puffin' Billy," also got remade due to it being a stock music cue as well.)
This even happened with Golden Book Video in the mid-80s, but not with Capitol's music. Their opening logo from 1985 originally used a modified KPM stock music cue, "Prestige Logo (a)" by Paddy Kingsland, but I guess to avoid having to pay the royalties each time they released a new VHS under that banner, in mid-1986 they replaced that music with a sound-alike fanfare that was apparently an original composition that was then used for the rest of the logo's usage (until 1996, at least!)