cause im pretty sure toei is known for like doing stuff like refusing to give quality masters of shows and stuff
and isn't sailor moon not available on bluray in japan yet? toei probably didn't want people reverse importng the series and stuff cuz same region for blurays is japan and usa
edit - fun trivia! toei once gave sony a very good copy of the transformers: scramble city mobilization ova for a release on the 2006 dvd release of the 1986 movie, but they didn't license the audio track, forcing it to have a shitty english commentary. but for the aussie and british companies that released the film, toei gave them the audio track, but the video quality they got was so poor, they literally opted to use a fansubbed copy they downloaded because that was actually better quality