A lot of people play less FAF because they reach a high shown rating that isn't necessarily representative of their current skill:
- Some people manage to get overrated and then don't play many/any rated games afterwards because they don't want to lose that high rating
- Similarly, some ladder players reach a peak ladder rating and just hold it indefinitely without having as much incentive to keep playing to be considered a top ladder player by rating
- Many other players reach a proper rating, but then stop playing FAF for months/years for other reasons, and when they come back to FAF, they are overrated and forced to lose many unbalanced games to get to a rating that is reflective of their current skill level (many of them end up re-quitting rather than going through this process, as having to lose like 30 games in a row can be quite unpleasant).
Increasing rating sigma slowly over time should help each of these problems and should encourage people to play FAF more.
So, to explain the rating system; shown rating can basically be thought of as "base rating (mu) - uncertainty (3 * sigma) = shown rating". The higher the sigma value, the lower the shown rating and the more uncertain a rating is. So, new players start at "1500 base rating - 1500 uncertainty = 0 shown rating". A typical player with a lot of games has around 250-300 rating uncertainty. Playing rated games lowers uncertainty to around 100-350 uncertainty as a stable level whose exact value largely depends on whether the player plays a lot of 1v1's (less uncertainty), 3v3's, 8v8's (more uncertainty), etc.
If we increased uncertainty slowly over time (such as by 1 point per day), then the shown rating of inactive players (and those who avoid playing rated games) would slowly decrease over time. The base rating would stay the same, but it would add incentive for players to keep playing rated games rather than reaching some peak rating and then barely playing afterwards. It would also help with properly rating players who stop playing FAF for a while, as their rating would slowly become gray/uncertain again if they don't play for a very long time. That would make it much easier/faster for returning players to get an accurate rating upon returning, and if they haven't played for years, their rating would even be gray, which would make the transition easier while being a fair representation of "rust".