Hello!
Not all airliners are RNAV approved and therefore must use raw data by law,...
Just out of curiousity: Where and how do those airliners fly? In my part of the world BRNAV-capability (e.g. RNP-5) has been introduced as a mandatory requirement for IFR flying from 1998 on. There were some exemtions in the beginning, but now you can't go IFR flying in a Pa28 unless it has an approved BRNAV installation.
Greetings, Max