Hilarious, when I told my mom I finally got a job, only part time, she said the exact same thing. Told me to start looking for a real job, because the part time was clearly temporary. And I take back my previous statement from the past chapter, it seems they were pretty supportive, I still hope they'll be accepting of their child's lesbian experience. Oh and wow, she has/had? friends, now I don't know if she's in a worse or better position than I am. And finally a fetish I can understand. MILF's are seriously under-represented in manga (not doujins), I don't get the japanese obsession with weird archetypes like tsundere, loli, and gyaru, I mean their obsession with high-school frankly strikes me as Unhealthy. I for one would be happy if I never had anything to do with a high school or anything related to a high school ever again.
I wouldn't group all of those archetypes together (I think some of it is just pdfilia), but at least with tsundere and gyaru, I think it's about expression. Japan is a very conformist society; there are like fashion cultures and trends and whatnot, but everyone is ultimately expected to take the same path down the line. It's probably cathartic to see depictions of strong social expression. It's no different than how we have manic pixie dream girls in the west, for instance. It is a bit more one-dimensional, but that's because of the aforementioned conformist society.
As for the focus on high school, it's escapism from the rigidity of Japanese adult society. I don't know if it's fair to imply that they enjoyed high school by comparing how you wouldn't enjoy reliving high school; I highly doubt mangaka and LN authors had a much better time in high school than you did. In fact, if they did, they wouldn't be so obsessed with writing stories about suicide in high school to be reincarnated in a fantasy world. I think it's more so that Japanese adult society is just even worse than their high school experiences, so they're looking to go back to the last simple time in their life and branch off their life, rather than relive it, hence escapism. There's also a pdfilia aspect but that's all of Japan tbh.
Anyway, we kinda have it a bit lucky in the western world; society is a lot more individualistic, so there's a lot more freedom for expression and spaces. Once we've gotten past the rigidity of school life, you actually get more freedom, unlike in Japan. If you had a bad experience in high school, you have agency to shape it into a better one in the future once you've graduated. The thing you can hope for is the freedom and acceptance of adult society. Sure, there are still exclusionary problems like racism and homophobia and bigotry (I'm not trying to deny yours or others' experiences facing oppression and exclusion, they are serious and problematic), and you can point to niche spaces in East Asia as parallels to the western world. Still, if you've ever lived there, you'll know that it's really not the same, and that it ultimately feels like you have more options, whereas in Japan, it simply gets more rigid, so even if high school was a crap time in your life, it's still the only time you can look to for hope.
So if we were to use a metaphor, life is like a tunnel and hope is light. The tunnel gets brighter for people in the western world, whereas it just gets darker for East Asian society, so even if the tunnel is very dark in the past, it's better to reminisce about the past and escape from there, since at least it looks brighter in comparison.
And on a sidenote, I'm ambivalent to milfs. On one hand, it can seem hot at times, with like a sort of mature and comforting vibe to it. On the other hand, it feels like it's a bit much with how it's fetishizing Oedipus Rex, grooming, and infantilization at times. I guess I'm just repeating what the author said, since that's also more or less how she feels about it lol.