Why was Michelangelo at first hesitant to paint the frescoes in the Sistine Chapel?

I believe it was because it was illegal sorry if I'm wrong

When Julius asked the esteemed artist to switch gears and decorate the Sistine Chapel’s ceiling, Michelangelo balked. For one thing, he considered himself a sculptor rather than a painter, and he had no experience whatsoever with frescoes. He also had his heart set on finishing the tomb, even as funding for the project dwindled. Nevertheless, Michelangelo reluctantly accepted the commission, spending four years of his life perched on scaffolding with his brush in hand. He would return intermittently to Julius’ monumental tomb over the next few decades.