You are working with him to create a solution and should ask questions from a shared point of view. Your questions instead sound like you are doubting him.
"How can this make our checkout page better?" "What benefits do other companies get from using React?" "Is it feasible to change technology at this time?" "There might be implications if we switch, like..."
You are not understanding why they should consider it; you are subtly asking them to justify why they are bothering you.