The heavens were paramount, and even Saints and Demon Masters had to act according to the will of the heavens. Defying the heavens would mean facing heavenly tribulation, which could obliterate one's body and soul.
What did it matter even if one were at the Genesis Tier? They would still have to face Immortal's Calamity once every 100 million years. If they couldn't overcome these tribulations, they would be cursed by misfortune. Thus, it would be useless even if they still had a lengthy lifespan—they wouldn't be able to escape the fate of death.
As such, the heavens couldn't be defied, nor could they be provoked.
However, just the name of "Heaven Crushing Alliance" was already offensive in and of itself. Moreover, the power of Genesis Tier Saints was intricately linked to the Regulations of heaven and earth. Thus, this was more the reason that they shouldn't go about defying the heavens.