More bugs than a mangrove swamp
One of the main reasons for this is that CS:S is, for all the simple brilliance of the format, a game full of bugs and glitches that make consistency within competitive play an impossible dream.
Indeed, if any testament to the potency of the format was needed, can you imagine a First Person Shooter game where the bullets all too often never arrive anywhere near the crosshair proving popular? Due to the way the netcode works this is an all too common occurrence and that isn't all that plagues the game.
The way the physics engine works allows something called "bunny-hopping", repeated strafe jumping that allows the player to gain speed and arrive at parts of the map before they realistically should, handing them a major advantage.
The way the models and their "hitboxes" – the point where bullets would register impact if accurately hit – are represented in relation to their movements is a continual problem. Trying to land a headshot on a bunnyhopping player is incredible difficult as the hitboxes tend to lag a fraction behind where the model appears.
When planting the bomb if you shoot at someone and they stop mid-plant they impossibly shift and warp, something that is known as the "crabbing" phenomenon.
There is also "crouch-bugging", an act that enables people to bob up and down on the spot so they can see over the top of an object, without their opponent ever actually seeing their head. All of these problems have had a huge impact on how people play the game and leagues find it incredibly hard to police them.
Can it be fixed?
Perhaps the bugs are not fixable, but you wouldn't really know one way or another given Valve's reluctance to be drawn on the issue.
Fixing the issues don't seem to be a priority and they have continually foisted improvements on the community that they didn't want or need, at the same time releasing updates for newer games in fast succession.
COUNTER-STRIKE: Source - do you think it can be fixed?
The recent 1.6 update that fixed similar problems that existed in the game came after close to 10 years hasn't helped the online community who have by now integrated the glitches into their play style. The key to making Counter-Strike great again is not to fix something that is so fundamentally broken and outdated that by the time it does all the things it should and could we'll be taking day-trips to the moon.
What they need to do is draw a line under what has happened and simply listen to the competitive community for what needs to be improved. The Source Engine was obviously not cut out for something like a competitive shooting game, where absolutes are paramount.
There is no chance that the average CS:S player will not move across to something new and improved because, and perhaps this seems bizarre, you won't find many with much good to say about the game.