The clutch hydraulic circuit is very simple, either it had air in it or you have a failing master or slave cylinder (if one fails you are better off repairing/replacing both as they suffer identical wear). If they are leaking, you initially get a full stroke as you push the clutch in, but fluid rapidly bleeds past the leaking seals, causing the clutch to begin releasing by itself. Unless you have xray vision, from the drivers seat it feels like the clutch release point requires less pedal travel - this is not the case. Even though you may be able to change gear without pushing the clutch right in, do not do it as it will be at the expense of premature clutch wear and possible transmission damage. Leaking seals are often only internal, so you may not see external fluid leaks. By the way, this is not a theoretical explanation, I learned the hard way several years ago.