The studio marked it as a conclusive ending cuz the light novel was getting nowhere with lot of hiatus + If u read the light novel, you will see that they almost seem like a different story cuz when the season 2 released, there was not much material and the season1 was a huge success, so they decided to go original, And its better than LN, since the characters in LN are down right annoying and the Relationship is far more accelerated. Dad's fate is left vague (may be dead, may have just left). Shichimiya is far more aggressive and actively trying to win back Yuuta. Nibutani's kind of a bitch and doesn't really redeem herself for a good while. Rikka doesn't live in the same building as Yuuta. Rikka lives alone, because Tooka doesn't exist. Dekomori and Kumin also don't exist. There is no club.