Because you are 15-20% of the Republican electorate and divided among yourselves, which is not a position from which you get to call the shots.
The "nominate my guy or I'll shoot this dog" strategy has gotten you nowhere, and is p*ssing all the other Republicans off.
That's why you have to settle.
We've heard the same thing in every election cycle since I joined FR. Doom and gloom, woe is us, to hell with the country if it doesn't agree with us. It's tediously familiar.