The really small provider is often here today, and gone tomorrow. With the distances involved, there's no risk that his customers will come knocking on his door.
A while back, even the "old hosts" were maybe 2-3 years old. Exceptions were 7-8 years. Now you have companies that have been players in the field for 15 years.
Then there's branding, which comes with size. As the Internet exploded in size, so have hosts. Some of the bigger ones advertise in very public places, so they become part of people's lives. Hosting is no longer a web only niche. People get that "I know this company from somewhere" feeling, which gives them a sense of familiarity, and, at some level, it becomes mixed with a feeling of trust.