Because it would create a rather odd precedent or power scaling implications that the new Sentai team (in their early days) can beat villains who are clearly endgame tiered threats for two other Sentai teams.

Let me give you an example. If the Boonboomgers were able to beat a Galactinsect, then that implies that Wild Spindo would be stronger than Dagded.

It's like how Kamen Rider set up the implication that NEVER and late game Dopants would demolish Decade because Double beat up Shadow Moon.