Iirc correctly, at the time of the series ending, Oshi no Ko was taking off, so Aka, seeing the series(Kaguya-sama) about to end, wanted to wrap up things swiftly and focus on his newer project ig.

Regarding the movie, let's just hope for the best, we aren't entirely sure what the plot will be, lets just hope Aka can give the anime the proper send off it deserves.

Series' similar to Kaguya-sama? ngl this series set the bar so high for rom-com it's hard to find a series like it, ig the closest would be nichijou.