First rule of assassination: kill the assassin.
Any professional hit team is going to understand that killing a high-profile political leader will make the team a completely disposable liability afterwards if the sponsors want to remain anonymous. Teams will not be inclined to take the job for any amount of money.
That is why recruiting a fanatical amateur and planning a "lone wolf" assassination project looks like a more successful choice, if the sponsors do not wish to be identified.
It is possible to find a team of professionals who may do a job for reasons other than money. Such people will usually want credit for themselves or their "cause", which can readily be tracked back to the sponsors.
Assassins are basically as expendable as the ammunition they might use.
See first rule upthread