Some people would criticize the fact that Wikipedia survives on volunteers as exploitation.
Wales keeps himself basically comfortable. He's upper-middle class at best. Compare that to Pichai's $10 million in total compensation last year, which is roughly ten times the lifetime earnings of the average American. Wales is closer to the pay of his volunteers than he is to Pichai, by several orders of magnitude.
Most people are willing to volunteer for organizations or efforts where the people leading the effort are paid a cash salary. It's when people get generational wealth off of the charity of others that it becomes offensive, at least to most people.