It may come from the early days of their career as doujinshi writers, perhaps due to the fact they were also fan girls once and so find in their richly shounen ai based plot linesan excellent means for channeling their fantasies, just as it happens with most of the doujin autors. Some can say it is their knowledge or belief smouldering bits suggest and seduce more deeply than straight forwarded depictions, the fact they want to keep their works elegantly above the ones that are plainly based on pages and pages of PWP sexual intercourses between two attractive males. Some may say they don't risk too much in order to keep their manga massive. The Suggestion Though populated with moments of erotic, physical tension between their male characters, those issues are always managed at the level of delicious innuendoe, and so we get to read how deeply involved a couple is thanks to the way their hands touch each otheer, alook of desire in their love-filled eyes, even the dangerous closeness of their lips. Deeper sex scenes always appear insinuated and never directly shown, and get to be assumed by the reader who in that way gets to knwo how the couple is bonded, complying to the wordless, pictureless play.
Tenderness is another way to suggest a swet, innocent erotism hanging around a couple.
Even in these cases the scenes are plagued with voluptuous symbolisms instead of going into straight forwarded sadomasochism.