Based on MyGMRS.com most of the repeaters in the areas that I travel through have the same settings. So, I programmed my radio for those settings. If it works, great. If it doesn't work, it doesn't work. MyGMRS is a fairly decent resource for finding GMRS repeater information. I will assume that repeaters not listed are not intended for public use. That is the option of the individual who spent the time, money and effort to put the repeater up. Is MyGMRS perfect? Nope. Do I care that it is not perfect? Nope.
I work with ag operations. They are not interested in sharing their resources with the public, the repeaters serve a business purpose for their family owned business. GMRS is a great solution. They do not need to spend the money on business itinerant freqs and they can coordinate larger area communications.