In an interview with Develop, Robin Walker discussed the reasons for making the game free.
"Over the years we've done a bunch of price experimentations with the game," he said, "going all the way down to $2.49 in our random one-hour Halloween sales.
"The more we've experimented, the more we've learned there are fundamentally different kinds of customers, each with their own way of valuing the product.
"Now that we're shipping it, it feels like a fairly straightforward next step along the "Games as Services" path we've been walking down for a while now."
It's interesting - the concept of a video game as a service. Valve has been hinting at free-to-play games for a while now, and it has rarely put a foot wrong when innovating in the past - it's hard to see how this won't be a success for them.
At the moment, Valve is clearly focusing on increasing the user base of Team Fortress and monetising the game through Micro transactions. If this move is successful, it may end up transforming the way first-person shooters on the PC are sold long-term.
Free at last [Develop]