Is the reason channelers get so many false messages about Ascension being imminent or other rescuing of humanity because they know there are only a few years left?

This is very much the case and fills in the gap you have puzzled over—how they can keep the game going for so very long with a very dramatic promise of events that would be unmistakable when they commenced, such as a transformation into a higher dimension of the entirety of humanity as well as the planet itself. Knowing human beings, they understand you become impatient as a species when forced to wait too long for a promised reward. Keep in mind however, that those receiving such messages are also being manipulated with mind control to keep them complacent. So this is another factor in their favor. People are not allowed to become very disgruntled because those behaviors are suppressed with respect to their manipulations and their strategies. But nevertheless, it makes this a realistic enterprise, to dangle the prospect of salvation and rescue and keep everyone hanging, because they know it will not be for decades and decades, that it will play out in their favor within a few years, and they can keep the game going easily for that length of time.