I got to think they would do so much better if between these message one evening like 'Let's meet' and then after a blank screen next day's message 'Wow, we had fun yesterday!' (like you wrote before) there was someting substantial, like more of a ususal scene in this bar with backgrounds and dialogues. And it's quite doable given majority of games are using Unity, Renpy or Unreal engine and a lot of them - AI, which can generate all sorts of scenes and backgrounds, like in Mila AI or Blurring the Walls, Shadow of Ambition.
But you'd need to opt for this - AI - strategically. Can get easy pick of some pics from real porn for faces and photos of fucking being sent over the phone, but there will be no flexibility for those scenes 'outside the phone'. And you can't mix AI and real porn, right?
But the devs either opted for real porn, or haven't thought about it or they opt for easy way of sticking to the phone format - you generate a few pics of faces, underwear and fucking each update (not draw or render, I mind you, generate) and add on top of that pile of text slop and rake in the cash, sometimes seemingly unreasonable pile of it given generated pics and forms of phone and buttons etc. moving from one update to another without any major changes. Guess you mostly have to write dialogues (text).
And text wise, or plot wise... It's kind of more substantial thing and more demanding than generating AI pics. E.g. I liked Netorase Phone when I played it some updates ago from the beginning, but now they write like it's been quite the sameish few last updates, just some new chars appearing to fuck your GF? It's either lack of some overall plan for the game and drifting plot-wise, or sadly the dev turned the milking mode (or maybe it's both).
P.S. And there were few messages here recently about possibility of using more of 'phone stuff' is usual games, RPGM made mostly? Messaging, photos. Think many started to do this after Scars of Summer, but it's kind of poorly made. There is a room for improvement here and I'd welcome that, generally a mix of some usual gameplay and these 'phone games' would look and play cool, IMO. More immersive maybe, closer to real life? Though it might be difficult to execute and resource consuming, like implementing a lot of that phone stuff using RPGM engine.