I love a lot of Japanese artists like JUDY AND MARY, Siam Shade, and I don't see them much present in music services. Is that any sort of Japanese "culture" or prejudice with these platforms?
Spotify or other music services can't go and look for all the musicians of the planet. It would be a huge job almost impossible to do.
Artists (or people of their staff) have to do the job of reaching these media and send their music. For example, this page Spotify for Artists explains for an artist how to have their music on it and how to manage it.
From my experience of my former personal band, we could have our music on standard music services (deezer, spotify, apple) and we are way less famous than your requested bands, so I'm probably sure that if these bands are not available, that's because they probably don't want to be in there.
Edit: Actually, I just checked and these two bands are available on tune in.
Licensing is the main concern for lack of access. It costs money to put the music in the streamable library and that money needs to be paid to the artist and the record label. Streaming services have to balance the revenues they get with the costs they have to pay in licensing so that will mean that they have to choose which songs they will license to put in their library.
Historically, this has been an issue with radio stations. Licensing costs can be expensive for radio stations because of the wide audiences they can avail that music to. Streaming services reach agreements with record labels by tallying the number of streams for each song.
Foreign music can be unappealing to streaming services due to the smaller listener base in the countries which those streaming services operate. This can mean that the upfront cost of streaming those songs (expanding hard drive space, initial payments for such rights and such) makes the purchasing of those rights dissuasive.