Because I love this child and he needs more love, especially his relationship with Yuuri ( ͡° ͜ʖ ͡°)
While Phichit is an incredibly friendly lovable cinnamon roll, he won’t stand for anything threatening his best friend Yuuri, even if the threat happens to be someone Yuuri loves. Yuuri clearly adores the Victor he knows now (just as much as he idolized the distant figure in the past), but Phichit won’t forget how much Victor hurt Yuuri in the past, unintentional or not.
I headcanon that on top of being a skilled figure skater, Phichit is an academic genius who skipped grades and entered college in Detroit super early where he met Yuuri, which explains their long acquaintance despite the age difference. He is very, VERY protective of Yuuri. I’ll put up a more detailed headcanon post later (and if there’s interest, possibly prequel comic of pre-YOI anime Detroit college days).