It's not a new trend... it's the way it's always been done
You do know some these shows are airing on tv too? Like u said if it was tv it was one episode per day. Kdramas and others actually air on tv for them so they cant post the episodes ahead.
Why is "ongoing" the new trend? Why can't they just drop the whole episodes. As a marketing strategy its working…
Some shows drop all some don't. Way back even when we use to watch direct tv and stuff, we had to not miss the time to see the new episodes of Adventure time. Never changed we still do that.