1. Because the theory is so unconvincing
Science isn't about convincing people - it's about describing and explaining what is, based on observation, theory and testing.
If it had to convince people, of limited or no expertise, and with wildly different levels of intelligence, then it would have to dumb itself down to such a degree as to be meaningless.
So instead of trying to make electricity, genetics or relativity convincing, science just makes the light bulbs switch on, the genetic medicines cure people, and the satellite navigation systems direct drivers.
If someone isn't convinced, that's fine - they're free to research and produce their own light bulbs, medicines and satnav systems.
Could there be any greater conceit, than for someone to believe that the universe has to be simple enough for them to be able to understand it ?