This is because animals are superior and closer to humanity than inanimate objects and plants, and Allah knows best.

As for the cause of their disobedience, it is because they were created from Ignorance (Jahl), doubt, confusion, disobedience, and darkness. This is confirmed and supported by what al-Mufaḍḍal clarified from the Master al-Ṣādiq (peace be upon them both) in the Book of Shadows and Figures (Kitāb al-Aẓilla wa al-Ashbāḥ), saying:

"O Mufaḍḍal, do you know why Iblis (may Allah curse him) disobeyed?" I said: "O my Master, you know best." He said: "Indeed, Iblis is Ignorance; he was created from ignorance, doubt, confusion, disobedience, and darkness, because they wronged themselves. He is in his sphere with nothing of clemency (ḥilm) or knowledge (ʿilm) in him; rather, he is dark, never emerging from darkness."

The necessity of His (the Exalted) plotting against the disbelievers Plotting (Makr) and deception (Talbis)

And denial, rejection, and disbelief. He will never return nor obey, for ever and ever, and for all time; and likewise his progeny, for they are from him and to him.