Truth be told, the overwhelming majority of the "scholarly work" that is published has little to no effect on the scholarly world. So if our motivation for being scholars is to change the world, then in all probability we are going to be disappointed. Recognition and changing the world are (very) occasional fringe benefits, but that's not why I write.
I write because I want to learn.
There are lots of academic institutions that prize very highly having a well-published faculty. That helps in attracting grant money, donors, and other well-published faculty. But mine is not one of those institutions. We say that we want faculty to be involved in scholarly work, but we define that so broadly that it is hard not to be involved in something that falls under that category. I'm not trying to change our policy, but just to suggest that we're kidding ourselves if we think that we're really learning new stuff or even keeping up in our fields if we're not writing about it. The process of writing forces us to think very carefully about a topic, to organize it in our heads, to evaluate strengths and weaknesses of positions, etc. Yes, we can do that to some extent without putting words to page, but there is a critical degree threshold that is crossed somewhere in the writing process, especially when you know others are going to read it--even more if there is a peer review process involved.
When we as teachers give writing assignments, they are not so much to check if learning has taken place as they are opportunities for learning to take place. We don't think that our students will really learn the material to the degree we want without synthesizing the information in a writing assignment. Do we think we're any different? There have been many times that I've read widely and thought about a topic to the point that I thought I had something to say. But then I tried to write about it only to find that I didn't understand it well enough yet to be able to explain it clearly. Then laboring through some writing helped me to really learn and understand it. That's why doctoral programs make you write a dissertation. That's why academic institutions (should) expect their faculty to write. That's (at least one of) the reason(s) I write.
Even writing this far-from-polished blog entry on writing has given me some more ideas about why I write. So I've added "Part I" to the title. Perhaps this will become a series of entries that try to sort this out.