It's unfortunate that Sony never bothered to take a chance on even one of these games. Attack of the Friday Monsters was very charming, but these seem to have a much bigger budget and I prefer the look of the characters in them.
Of course they'll say the cultural differences are the main reason they didn't localize them, but I'm sure it would have found a following had they done it.
SCEA/SCEE of yore never even took a chance at more 'mainstream' games like Wild Arms and Arc the Lad, much less BokuNatsu.
Many Sony-published games of Japan in the PS1/PS2 era were actually published by 3rd-party publishers like Working Design and Bamco. Demons' Souls is probably the most well-known example of this in recent years, where America/Europe doesn't what Japan does.
BokuNatsu was so niche that even 3rd-party publishers didn't care to publish that franchise in US/Europe.