If you look at the results, you will notice that Manjaro is not the most popular distro for people who use the phone as a daily driver. This indicates that people who keep Manjaro are less likely to actually use the Pine phone as a phone.
So it seems that the reason it is the most popular is that is the default. If you look at what interface people like, the default (Plasma) only scores 21% in that poll and it falls to 18% amongst those who use the phone as a daily driver.