The Vatican also had real power back then, not just soft power as the head of a religion. They controlled a decent chunk of Italy outright. Galileo was also around during the Counter-Reformation when the Church dealing with the political ramifications of the rise of Protestantism, and saw his reinterpretation of the Bible as fire power for the Protestants.

Moreover, there were valid epistemological criticisms of Galileo’s theory. The scientific method and accepted standards of proof were being developed. This work was also pre-Newton, this physical laws themselves were still not well-understood. Many of his critics were skeptical because, while heliocentric theory simplified the math, Galileo hadn’t disproved geocentricism — he gave a sufficient condition for his data not a necessary one. Thus, they complained he was making claims beyond the scope of his scientific work.