Why would I set it free, you ask your monitor because you don't understand how the internet works?
Because it's a good idea from a business perspective; give the world a free taste and hopefully they'll come back for more.
Because it potentially means more exposure.
Because I hope with the added volume I'll get a few more reviews.
Mostly though, I did it because I can. I get a kick out of people enjoying my creations, and this way there's no barrier to them doing that.
As soon as you make your scribbling available to the world, writing becomes a business. I get that. I'm supposed to care about marketing, and keywords, and BISAC codes, and which farm animal is most appropriate for literary sacrifices. Sometimes I do care about those things, and it makes me sad. Mostly though, I don't give a shit.
Writing a novel and releasing it into the world is a joy; from the raw creative release of the initial words-on-a-blank-page stage, to building and preparing the files for upload, to having someone tell me they enjoyed it. I get a special pleasure from putting together the paperbacks, and there's very little chance I'm going to sell a bunch of them. I do all this because I enjoy it, because I want to share my worlds. Setting The Bridge free means more people will get to see it and let their minds play there the way mine does.
I'm also giving away the sequel, The Algorithm, to anyone who signs up for the mailing list. Because I don't like money, apparently. I'll do a banner for it or something when I get the time, but basically all you have to do is sign up and I'll send you a link to the file. This means that, for a limited time, you can get both books in two minutes, for free.
Go read a book (I suggest mine, which is free)