Every time the clutch is depressed, the release bearing pulls back when retracted some of the fine clutch dust (no seal keeps it 100% sealed as far as bringing in dust, even w/out leaking fluid. The dust is extremely fine in micron size) contaminates the fluid. This then thickens over time as it is subject to the heat from the drivers side exhaust manifold the line runs along. There is a drill mod where you can drill out a restrictive orifice, but this effects all modern hydraulic clutches with GM the most common we see over the years.
Many aftermarket clutches as hypurone shares that come with a new better designed release bearing (throw-out bearing) that helps prevent this, but it is a design issue as much as anything else. Do a Google search on "clutch pedal sticking to floor".