Why was my relative’s Japanese tourist visa application denied?

Hello! I just wanted to get your thoughts or if you have any idea why my relative’s Japanese visa application was denied based on the facts below:
– He’s from the Philippines btw.
– I’m the guarantor of my relative in Japan and I have a long term resident status.
– Last June, I was able to invite my relative to come to Japan. He was given a 90-day tourist visa although he only used 70 days (his actual stay was from June to early August)
– After his Japan trip, we tried to apply for another 90-day tourist visa in September, but unfortunately, his application was denied. It was supposed to be from October to December this year.

I understand that the Japanese Embassy does not disclose the reason(s) for denial, but I was wondering if you have any idea why his visa application was denied based on the above information. Thank you in advance!

by bubblewrap27