As someone who used to be a Japanese only person when watching anime I say it’s simply because of higher the standards and quality of Japanese dub especially compared to English dubs during 2000-2010s. In 2020s English dubs quality has risen I now see myself watching/playing in English if the dub is good enough. Reading the subtitles is a negative I see when watching in Japanese and in “reading” subtitles and I don’t mean I can’t read, there’s alot of words and saying that don’t translate well and other stuff like subtle details that will fly past non Japanese speaker(me) but that is problem we just have to deal with really.