Why did some mathematicians doubt that Guglielmo Marconi could send radio signals across the Atlantic?

Some distinguished mathematicians doubted that Guglielmo Marconi could successfully transmit radio signals across the Atlantic Ocean because they believed the curvature of the Earth would limit the practical range of electric waves to approximately 161–322 km (100–200 miles).1

At the time, it was widely assumed that radio waves traveled in straight lines, which would cause them to move out into space rather than follow the Earth's surface over long distances. Marconi, however, possessed a great capacity for perseverance and a willingness to challenge prevailing expert opinion. He ultimately proved the skeptics wrong in 1901 by successfully receiving signals in St. John’s, Newfoundland, transmitted from Poldhu, England. It was later discovered that the ionosphere reflects or refracts radio waves back to Earth, allowing them to travel far beyond the line of sight.231