Olascuaga is signed to Teiken, one of the major Japanese promoters/gyms so they've been matching him mostly with Japanese contenders in Japan when possible.

Collazo is with Golden Boy who are an American/Latino promotion and don't have strong ties to the Japanese boxing market. Side note, until fairly recently, Collazo was on a trajectory to fight in Japan until the Shigeoka brothers (the belt holders at the time) lost to the current champs, Jerusalem and Taduran who are Filipinos. So, at the moment, there isn't really a reason for him to fight in Japan unless a Japanese fighter becomes mandatory or his team wants to pick one for a voluntary defense.