Cause in PR, it was the Pink Ranger's zord. Iirc, had one in show appearance that way too when they used the toy for some shots.

The model kit is for Kaku though, not PR season 3. And since it's a model kit, for the few that do want that, they can paint it to match. Minipla has done that before with things like Gokai Submarine in all black. Or Gokai Green's racer in all black. At least this is white plastic so it'll be easier to paint.

90s BoA was kind of all over the place on weird decisions sometimes.

I think the deal with the Pink/White Shogun Zord is:
It's white in the original Kakuranger footage, re-used Kaku footage for MMPR, and in the show, it's a shared zord between Kimberly/Kat and Tommy. That's why they share the cockpit

It was recoloured Pink in the toyline, to have all the OG Ranger colours there, but since the toys were used to film the Shogun Ultrazord footage, it also shows up there. Basically, the zord flips colours when they summon Titanus.