Here's why:
* Sulfonates contain the sulfonate group (-SO3-), which has sulfur bonded to three oxygen atoms.
* Sulfates contain the sulfate group (-SO4-), which has sulfur bonded to four oxygen atoms.
Sodium C14-16 olefin sulfonate has a sulfonate group (-SO3-) attached to a hydrocarbon chain. This makes it a sulfonate, not a sulfate.