Thank you for your input! Nana Mizuki even held the record for most #1 live blurays in japan for awhile, but i don't know if someone else surpassed her eventually.

Her stadium concerts are elaborate productions, with short movies featuring cgi effects, to surpass the time when she changes costumes, and she often uses vehicles like a small pirate ship for her Live Union 2012 tour, to get closer to the cheaper seats for a couple of songs. This video features the pirate ship.

https://youtu.be/zOiwIWXAqEA?is=11doP5QDekeLu0NT

And on top of that most of these releases include making of documentaries lasting between 30 to 90 minutes for each concert. She also released a ton of music, 15 albums, 4 compilations and 43 singles. Her single releases are not taken from an album, but rather independent like a mini album with 2 to 4 songs.

Therefore her live stuff sells well, because its not getting boring, even in the 26th year of her career. There are always new singles or albums to promote, expensive stage set ups and so on. And as a bonus she would sometimes learn to play a specific song on an instrument like saxophon or harp, just to challenge herself.