With JJ Lin, I think they 'met' through a mutual friend and he was asked to make a song.
https://syncnet.work/archives/22788
In this case, I wonder if it's related to a Chinese event or something due to the fact that it came up last year and the opportunity came up again and I think MY ALL was chosen because it's basically her new Who...? She's had a few like RED LINE though too but MY ALL is the one that has persisted through the years.
https://www.instagram.com/koshints/
Koshin seems to be involved too as a CN/JP liaison. He's worked with a bunch of Japanese and Chinese artists it looks like. I actually remember when he first did the song Piledriver for Do As Infinity!
https://www.ksentertainment.net/work
https://ja.wikipedia.org/wiki/Koshin