I do understand this sentiment and I think the popcorn-movie comparison is apt. It's just... there can be so much more. "1Room - Runaway Girl" has a very short but cute story and its decently written. "Accidental Mind" has a great story as well. Even very fantastical stories like "Headmaster" can have crazy things happen without stretching my suspension of disbelief too much by simply taking the time to show how you can go from a normal world to an "ecchi" one.
I think that's what's bothering me most about it. There's clearly talent and effort that went into the very cute artwork for Summer Memories, as well as the overall game flow, but then the devs dropped the ball hard on story and characters. The loss isn't a minor one either IMO, because good writing makes the fantastical lewd stuff more erotic than just "Oh, I guess we're having consequence-free sex now!" Where's the tension and guilt after Rio starts her younger cousin's sexual life? What if Yui's motherliness was amped up, and her scenes start more intimately than rudely waking her up with a titjob? Have Miyuki's self control start to slip as she boosts her ego by teasing her nephew? Taking a little more time to develop these stories and characters adds more context to the sex, which is what makes a game's potential so much higher than an ass-blast of porn gifs or some shitty JAV. Why are these characters having sex? Don't care, doesn't matter, press LMB to cum.