That's because finding the correct definitions of concepts is a big part of the problem.

I wonder whether it's because they don't realize the problem with not being specific, or whether they are aware of it, but they do it anyway as a part of some signalling game. And what specifically would be the rules of the signalling game? It is merely: "If you don't understand me, it means I am deeper thinker than you?" Or something more sophisticated, like: "You can understand me, but to do that you have to read a lot of my texts very carefully. People who admire me are more likely to do it than people who don't, which is how I increase the ratio of people who agree with me among those qualified to discuss me"? Yet another option would be that philosophers use multiple channels for communication. Maybe they speak clearly and define their terms when speaking in person, but have a taboo against doing so in writing.