Because unfortunately everything both animated and in manga ends around volume 2.
After that, 95% of the series is on LN only, and anime and manga fans won't read shit unless at least 75% on screen is actual images instead of words.
And even with that, this series is pretty niche to LN readers, Haruhiro's POV is interesting but doesn't please at all people looking for selfinserting with a harem of cute girls because he is so insecure about everything all the time and doesn't want to get into a relationship with no one because he thinks shit might get bad later (and he was right).
Ranta is also a hypocrite as much as a an annoying bitch, and Grimgar unfortunately is the kind of series to do something good with him after like 18 volumes after.
This series is great, but its simply to niche, and there will never ever be a season 2 because the original studio refused to work if the OG directior its not working on it, and its been already a fucking decade. And if there is, any sort of quality or detail will be automatically subpar to the point no autist will ever feel satisfied even if Madhouse was in charge.