John Travolta's character

All of the "men" in that movie were basically Mama's boys. Notice their crappy diets and penchant for cheap ass beer? Unless there was a woman home prepping a meal these guys spend all day stuffing chew in their cheeks and drinking beer. Some would call it Redneck living but these guys weren't even rednecks they were urban laborers just as much as any urban male outside of yee-yaw Texas culture. The movie does a good job showing us how the Good 'ol Boy network runs deep in Texas as Bud didn't really have any advanced skills thus needed his daddy's connections to get a grunt job at the refinery.

Biggest reason? The writers needed him to be that way. But in all seriousness, he was a real cowboy from the country. Unlike the "urban cowboys" of Houston, Bud had actually grown up on a farm and could walk the walk. At the time this film was made, cowboys and other "all American" male types were huge in pop culture. Women were fascinated by them and a lot of men tried to imitate them. It wouldn't have been unusual for the local women at a place like Gilley's to be interested in a "foreigner" like Bud.