The elements are different. Typically “conspiracy to commit X” requires some number of people agreeing to do X and then someone from the group doing at least one overt act in furtherance of that agreement. So you can be guilty of “conspiracy to commit X” without ever getting even remotely close to doing X.

So for example if two mates talk about that they are going to kill person Y, that is the agreement. And then one of them buys a gun, that is an overt act. And even if person Y has very good security, and the two dudes have no chance in hell of murdering Y ever, that is still a “conspiracy to muder” charge.