I’m not especially a fan of George Strait, but I think his appeal is that he sings real country music. Traditional country music fans have long been plagued by pop and rock-lite music infiltrating their genre. Sometimes they’re unreasonably uptight about it (Charlie Rich), but there was valid concern that traditional country music was being pushed out. George Straight, followed by guys like Ricky van Shelton, later Alan Jackson, and to a lesser extent Clint Black, played a big part in keeping old school country music alive and fresh.
Ricky van Shelton may be one of the traditional guys who was pushed out by the new guard, though he had some personal issues and a label conflict as well. Black took some time off. Alan Jackson mixes it up quite a bit more than Strait, though I think the traditionalists still like him a lot better than most of the other guys on the radio. George Strait is the most traditional country of the neo-traditionalists still getting any airplay. He also is incredibly good at picking songs that are country, appealing, and appropriate for him.
As for just standing there, that’s what traditional country music is about. Garth Brooks has taken some heat from old country music fans for his on-stage antics. Hank Williams didn’t run around, why does Brooks have to? Strait’s from Texas, he wears a hat, and he dresses like someone’s dad. There’s no sense he’s in any way phony. He just stands there and sings because that’s what everyone’s there to see. It isn’t at all an issue with the demographic he’s after.
Basically, I think he came along at the right time, has talent, seems genuine in a sea of fakes, and has incredible business and musical sense. That’s his appeal, and his longevity.