Hitmen at the paygrade seen here absolutely do exist, you just usually don't notice that very often unless it's either secret services that are involved (e.g. Russia's various assassinations in the UK or Germany) or it's major figures assassinated by drug cartels who are not members of some sort of cartel (e.g. the murder of journalist Peter R. de Vries). Drug and other organized crime networks routinely kill each other, but it doesn't make the headlines if it's not done in the public.

You don't believe hitmen exist?

AKA "Contract killings" or "murder-for-hire". They are estimated to account for about 5% of murders.

They do, but the targets are rival drug dealers etc, not megacorp CEOs. (Except maybe in Russia.)