This is nowhere close to true.
I am willing to grant you that a random person off the street is more likely to have heard of Turing than Shannon. But much more likely still to have heard of Stephen Hawking or Jane Goodall or James Watson.
Public awareness of scientists drops off very quickly. That’s just the way life works. It’s lucky enough if random people off the street have heard of small countries or political leaders of their own country. Most people don’t remember most of the major genocides of the past few decades.
Shannon is without question one of the best known (by the general public) 30 or 50 scientists of the 20th century. It is ridiculous to pretend that nobody has heard of him. At the very least anyone with a STEM degree will have some idea.
But not everyone can capture the public imagination the way (say) Einstein did.