Not trying to sound dickish (really I'm not), but I actually already understand how the impeachment process works, and what the political realities are.
My point is more about releasing the evidence. If the smoking gun exists, or if a case can be made, then I'm curious as to why they (whoever THEY are) aren't pushing forward with it. Trying to first instead slowly build a case in the court of public opinion is risky -- the more time the Trump administration has to become entrenched, the more opportunities they have to build support within government and among the people. It's a gamble to hold off and hope that he hangs himself in the meantime with his own hubris, and he can still do a lot of damage in the intervening time.
I can only assume at this point that any evidence that his enemies have gathered is not incontrovertible.