I expect the motivation at least for the Cubans, is related to their eligibility to AOS via the Cuban Adjustment Act. Since many people believe the Biden program was illegal, then people using it would not meet the "inspected and paroled" requirement to AOS. That is just spit balling, but it is clear that many feel that Biden's program was unlawful to begin with. As to the others (Ukrainians, Venezuelans, Haitians), I don't believe they enjoy the same benefit to AOS as the Cuban do, but I could be wrong.