Hizuru wasn’t a reliable ally, their support was only agreed to on the basis that paradis agreed to zeke’s 50 year plan (which we know isn’t a reliable plan at all) and they even stated themselves that they would withdraw support if it seemed like supporting paradis would threaten their own country (very likely considering paradis is enemies with the world). Hell they made things worse by limiting paradis’s ability to trade with other nations in order to keep those resources to themselves.

A good chunk of the anti-marleyan volunteers were conspiring with yelena to activate zeke’s wine plan, and even those that weren’t would not have the social influence to convince entire nations to join paradis, unlike Willy Tybur who spent years building enough influence and a strong social standing throughout the entire world that he could convince nations worldwide to come together and form a global alliance to destroy paradis.

All of this still ignoring the fact that they had no time, even assuming that they COULD build strong relations with other nations, they only had 4 years before the world attacked them (something that would have happened regardless of eren attacking liberio) which is nowhere near enough to time to ease tensions built on thousands of years of history.