Amongst the many types of professional writers, there are grant proposal writers. There is nothing about that job title that tells you whether or not they would be able to write a good book. It also does not tell you whether or not they like their job. High quality grant proposal writers can earn a good living doing so professionally. Many of those that do, may have not had any idea that would be what they would do for a living. I do not have statistics that analyze exactly who gets into that after getting a writing or English or Communications degree and who just ends up in their 8th year in an admin job in which they are just glad they can pay the bills without getting their hands dirty at the office.
Grant proposal writing like resume writing, can work for some people. People can get into it as volunteers or professionally. A lot of creative writers would cry if they were limited to earning money writing in either of those ways. That is a lot like when sales people tell new recruits “Yeah, its great, you get to meet a lot of people.” That is not a bald faced lie but is misleading.