Or they just thought Yuuna wouldn't sell and then the license got snatched away. Or they just hesistated for too long and the license got snatched away. I doubt there was an active decision here in the vein of "Oh no, this manga is too dirty, we will deliberately not pick this up!"
No, they pretty clearly did make an active decision along those lines. For years they never picked up To Love-ru or To Love-ru Darkness, despite their success in Jump and Jump SQ. Eventually when Viz began their "Jump Start" thing that translated the first three chapters of each series starting in WSJ, they notably skipped some ecchi heavy series, starting with skipping Lady Justice while doing the rest of the batch. When Yuuna and Kimetsu no Yaiba started in early 2016, Kimetsu had it's inital chapters translated as part of Jump Start while Yuuna did not. Finally in 2017 Seven Seas licensed TLR and TLR
arkness in April. In July Viz licensed only Kimetsu no Yaiba despite both it and Yuuna having survived in Jump. Then months later in October, Seven Seas announced it's new Ghost Ship imprint while announcing that it licensed Yuuna and World's End Harem(which launched a few months after Yuuna and Viz had ignored entirely despite being one of Jump+'s successes).
All in all there's a pretty clear pattern of Viz avoiding licensing or translating heavily ecchi series, even if the series is successful in Japan or would normally receive a trial translation as part of another policy. I don't buy that they hesitated for too long either seeing as they announced they officially picked up Kimetsu months before Seven Seas announced it officially picked up Yuuna, when Kimetsu started one issue after Yuuna. Especially not after they "hesitated" for so long for TLR. That they thought it wouldn't sell isn't much of an argument either, seeing as Seven Seas clearly thought those series would(other than Lady Justice which failed in Japan and has yet to be licensed by anyone), and would appear to be correct seeing as they've been steadily releasing them.
So yeah, I'm certain there was a policy of avoiding the series with too much fan service. Which may or may not have changed with the advent of Mangaplus+. Bokuben's no measure as it's first chapters made it clear it was going to be more like Nisekoi than TLR in terms of fan service. Undead Unluck might be an indicator, but it remains to be seen going forward if it's going more for ecchi or more for comedy.
