I guess it because: 1. Japanese dorama is not so popular as K.Drama. Include in Netflix curator's mind :D Even if a dorama is so great...but it will be a miss. But at least you can still find good rating / popular dorama in VIU (a few). TBH..dorama have quite little place in many legal streaming site. the streaming site is now dominated by kdrama and c drama. dorama and thai drama are on same level now.
2. its cinematography doesnt meet Netflix's standard. Many good cinematography doramas was produced for both TV and streaming site. Some people complained about the quality of dorama, the story of dorama is usually great but the visual is dull. the tv dorama is like a filler whereas the CF is the main show in tv. you are probably know that cf/advertisement in Japan is a top notch. Compares to KDrama that aims to be a great show visually and story, it no strange if it passed Netflix's standard. It makes Netflix wont hesitate to buy licenses to stream Kdrama. Still, Netflix does its custom to co-produce drama with local korean producer and director, of course, with Netflix quality standard.
the translation and subbing matter for dorama is no problem for LEGAL STREAMING SITES. there are tons of paid translator. and those sites have money.
btw I guess Kissasian is an illegal streaming site? CMIIW not sure if they have a translator team. I had watch some vide with engsub there and find the translation is copypaste of subtitle made by fansubber. many illegal streaming just ripped off fansubber works. what so upsetting is.. they dont pay the fansubber for their hardwork.