
Yes there were. Older stories didn’t have much plot just romanticizing family relationship.
But nowadays I see a great plot with a sudo like incest relationship. Author cooking great plot with their degenerate preferences. I really want to enjoy the story through n through but it gives me sour aftertaste.

Well, it wasn’t really common like now. And I specifically pointed out "sudo like incest"... Back then only deranged publications were publishing incest stories. But now big publishers also start doing it and authors who can't directly add incest story, they used "sudo like incest" concept, so that there story doesn’t get censored.
And rare and common is not the same word. Back then only 1 out 10 stories you find that kind of plot but now it is 5 out of 10 or even more.
Nowadays, why authors are obsessed with sudo like incest? Specially in BLs? It just ruin the plot most of the time. Great plot, great character, great psychological war then author decide "lets insert siblings, uncle-nephew, cousins romance. I mean why? Even if they are not blood related, it still feels icky.