That may be true for your everyday murry furry who only likes adult art xD

But there are people who like romantic art :')

Also, if it is a "romantic ych" thingy, it might not appeal to people because they would prefer something of their own xD

I've made special YCH, but not "your character here", but "your couple here" with both characters at once :D

People were not interested I guess?

It is a bit more difficult to find people for this kind of pic I think xD

Most just want to sex. But if it is only that the whole time it will get boring. Some nice clean art is good too!

I don't think "your couple here" pics are likely to work sorry, two reasons for this I see:

1) I know if I was in a relationship and was getting art of us I'd want it to be special, I'd want to take my time and come up with the idea myself so it was meaningful.

2) You have very detailed YCH's and state that there are to be "No major character changes", well that seriously reduces your market [even if it was a sex scene with people bidding on each character] as that not only requires a couple, but a couple with the correct species.
- You might not consider certain things to be "major character changes" but without more information people may be put off immediately by thinking you won't make the necessary changes to make it look like their characters.

I see your point about 2, i'll do more clarifications about that

I believe it has more to do with Economics.

Instead of the usual two separate people pay for the one respective slot for themselves. This bidding style makes one person bid and pay on both slot. You could say "well the couple can pool the money together" - which is true, but not with Paypal where one has to sent the money to the other couple first, then to you.

Also the losers like me that have no actual significant other usually has to scramble to find a friend to join in.

It's more that I see these things at bad times for me. Besides, I prefer giving out my own ideas rather than accept a ych thing.