For fans of the manga, it's because they want to see the culmination of Yuzu and Mei's relationship (before their marriage at least) and see them have a truly intimate moment where there's no more hesitation between them.
That does seem like a pretty big misconception of Yuzu and Mei's characters though. A huge point about the series is how important true love is and how it is more important than simple carnal desires. Yuzu and Mei relationship did start physical but it quickly moved into being about the two of them connecting in a way they didn't with anyone else.
That's a good point. Most of their interactions in the early volumes were back-and-forth kisses led purely by uncontrollable desire (or in Mei's case, just screwing with Yuzu). But of course, we had the occasional heartwarming moment like Yuzu helping Mei with her father, or the bus stop handholding scene.
Then in the later volumes, they began spending more time bonding like the Student Council arc, the date, trying to read each other's feelings in Volume 7, etc. As time went on, and the two fell deeper in love with each other, kissing became something more difficult because it meant so much more to them at that point. Speaking from experience, when you don't understand how love works, kissing someone you like, even while you're dating them, is far from easy.
In my opinion, I'm glad YuzuMei kisses are more infrequent now than earlier parts of the story, because it makes those moments all the more special.
