These two situations are not equivalent. A book author has basically 100% market monopoly on his/her books. He can set a high price and people who want to read

These two situations are not equivalent. A book author has basically 100% market monopoly on his/her books. He can set a high price and people who want to read the works will still pay. Whereas ride sharing companies interchangeable and are in full competition with each other, which, in a healthy market, should bring the price down to the point where they're all only making a marginal profit. The cost of alternative mode of transportation does not come into equation (well unless it's overall cheaper and better - then it will kill the entire market segment).