After looking through seasons 1 and 2 of 7 Seeds I have some theories as to why season 3 of the anime has not been announced yet.
After season 1, which was produced by Gonzo, Season 2 of the 7 Seeds anime was produced by Studio Kai after Gonzo transferred some of its anime to Studio Kai, so this studio could have other projects hence why they haven’t started or are delayed on work for 7 Seeds season 3.
7 Seeds season 2 was released in March of 2020, which was around the time when Covid-19 began. Although other anime studios have been able to release their works during the pandemic, it’s probably because they have more employees or they are just able to start new projects, Studio Kai so far has 45 Employees and are currently working on or releasing animes that are not ONAs.
https://en.wikipedia.org/wiki/Studio_Kai
Therefore it stands to reason why Season 3 of 7 Seeds may be delayed, the new studio may be capable of making it, but are delayed right now due to new projects with the current 45 employees they have now as well as the pandemic and the fact that the 7 Seeds anime started with Gonzo before the studio transferred its anime to Studio Kai.
What do you think? Comment below.