Luna clearly was the main love interest so far though.
It's very weird she only got 1 new event while Gracie suddenly got 9(!) and the others 0(???).
You're not taking into account couple of things though:
1) The game has 4 main LIs, not just one.
Sure, Luna is definitely my favorite girl in this game, and "My name is Luna" gave many folks impression that she's the main LI with how impactful it was, but as Cabin Fever said above, objectively it's not true.
The other girls (Gracie, Isabel, Cordia) don't have any events that are equivalent to My name is Luna, but that doesn't make them any less of main LIs.
2) Game always releases content in rotations.
Hopes always releases content in main story/main events → girls freeroam/lewd events → main story/main events → girls freeroam/lewd events →........ and so on.
Before the v0.07 (contracts gameplay overhaul update, which had 2 main events), last girl to get content was Isabel, which included her events of reconciling with Gracie as well as the Netori events.
And before that was a main story content update, and before that was Luna update with My name is Luna; which is one of the longest events (if not the longest) out of any of the single event so far in terms of length.
It may not seem like it (due to how long the last 2 updates have taken to release), but given Luna and Isabel had both gotten updates in terms off content, it makes sense for them to get much less content compared to Gracie, who hasn't had a proper update for couple of years now.
3) Content is based on what Hopes feel is right for the overall story, whether it's the length or amount.
When I finished the v0.08 update, Given a big influx of events for Gracie (9), I half-jokingly said to Hopes the following, and he gave me a reply:
So as he said some girls may have more at times and some may have less at times.
It will all depend on his planned story.