Actually I think you were right even if it was sarcasm. Specifically yuri usually tends to make them get together in the first chapters and then explore their relationship or have them be together from the start (Kase, Hana ni Arashi) or making them be together at the end and then end it right there. Finally, there are stories that do show the whole process of falling in love/getting together and then a few chapters about them being an official couple (usualy the last volume), like ygkm or girl friends, although I can't remember when Akko and Mari got together (chapter 27, end of vol 4?)
I understood "inbetween" as showing both the falling in love/getting together and the aftermath of the characters as a couple, as in, actually getting volumes that focus on the couple now that they are official instead of just a few chapters. But I do think it's not done that way for a reason and I understand writers. Not sure if there are examples of this in shoujo though, haven't read enough of it.
Well no, that is not a yuri specific thing. It's the most common thing in all versions of romance, from het to yuri to yaoi. That's just a popular story structure.
The reasons can be varied, but for one it is simply easier to generate drama and interest with the "will they get together?" plotline. Especially when more rivals are involved. It's actually pretty lazy.
Starting out as a couple has its own advantages, for example most of those stories start with them getting together without knowing each other all that well or to try it out. That basically just moves the "get to know each other and develope chemistry" part from the usual build-up to the confession into the timeframe after the relationship begins. But unlike the former they are allowed to go further in some aspects, as they are already a couple. There are also different issues that come up, but essentially it is still the harder version, because you actually need to generate original drama beyond the premise.
If you choose to build up to a confession and then go into the relationship, you simply already reached the peak of the drama and pay-off in the middle of the story, because authors rarely have the creativity to come up with meaningful drama after that first peak. And going from drama to feel good slice-of-life is even more jarring.
But yes, it happens. Takes just more skill.
My bad for mentioning citrus, I didn't mean to cause shitpost (I'm glad it didn't turn out that way) :v
Nezchan forgave you... for now. Always stay on your toes.