Why has the number of games decreased over time in WCC? The World Chess Championship between Lasker and Capablanca in 1921 was organised as the winner would be the first to 8 points, draws not counting, and if this goal was not reached, the player with more points after 24 games would be declared the winner. Lasker forfeited after 14 games.

The winner of the World Chess Championship between Karpov and Kasparov in 1984 would be the first to achieve 6 victories. The match was suspended after 48 games.

Those are only two examples of extremely long scheduled matches with many interesting games. However, nowadays the matches are much shorter. The 2013 World Chess Championship was scheduled to be only 12 games, and the last two were not necessary so there were only 10 games!

Is there any particular reason why the matches are now much shorter?
I don't think there's going to be a definitive answer for this: Terms are decided largely by FIDE with a small amount of input from the incumbent champion and challenger, meaning that people like us can't really know. I can however highlight a few factors that I think play a role.


As GuRoux hinted at, not running over other tournaments is a plus. Not just because of divided attention of the community, but because it means that at least two (and likely more, considering the role of seconds) of the worlds top players won't be able to compete in any other tournament while the WCC is ongoing.
Attention span. As an extreme example, the 1984 championship went for 48 (not a typo) games before the match was called off by the president of FIDE. It's hard to expect players or spectators to put aside such large amounts of time when there's no garuantee of a result, and people who are not really 'into' chess will likely stop watching quite quickly.
Increased costs. Aside from the high costs that are present in all post-Fischer-era matches (venue, hotels, prize pool, etc). there are a number of other expenses that have come up in recent years. To give only one example, the current (2014) match between Carlsen and Anand is being streamed live to the internet, which requires a production crew (streaming like that is harder than it looks) and commentators (I can't imagine the experience and quality of a top player and commentator such as Svidler coming cheap). It's true that this allows for advertising possibilities which might cover those costs, but that means that you need to find even more sponsors to cover both new and traditional expenses, and with more sponsors you can ask for less money as they share less of the limelight.
The format promotes attacking chess, in much the same way that 20/20 cricket promotes high-risk/high-reward play over the traditional test match format. The aforementioned Karpov-Kasparov match went for 48 games, but at the conclusion the score was 5-3 (five times as many draws as wins, and the ratio was even worse but for the last two games). Even people already interested in chess would likely lose interest with continual draws, not to mention attempting to attract new players. In a shorter format, you are forced to go on the offensive, because there is less time to make up a mistake arising from a mistake after passive play. Tiebreaks with decreasing time controls also means that the luck factor increses there, and so both players will likely want to avoid that.


In general I agree that 12 games is very short, but it's almost inconcievable that at 24-game match would occur these days, and even 16-18 would likely be stretching things considering the chess world's continued problems with finding and maintaining sponsorship.