You can, and Digicel sells prepaid SIMs at Port Moresby airport and in town. The catch is the registration. PNG requires SIM cards to be registered to an identity document, so you queue, hand over your passport, wait for the paperwork, and only then get online.
A travel eSIM skips that. You install it at home, land at Jacksons airport with data already working, and can order a car or message your hotel before you have cleared the terminal. For a country where arranging pickup in advance genuinely matters, being connected on arrival is worth more than the few dollars saved.