All airlines and travel agents do. A reservation is created in order to obtain a price quote, which quote is valid for a limited time [which, depending on airline or agent, you may be able to extend by paying a "Fare Lock" or "Price Hold" fee] during which time payment must be received; some time later (it is not always instantaneous on receipt of payment) an e-ticket is generated.
It is not the generation of the e-ticket that creates the PNR - the pre-existence of the PNR is necessary before you can even get to the situation of having an e-ticket issued.