Many country artists have their roots in Bluegrass. Most of these artists still enjoy the music as much as they enjoy their contemporary country sound. This may be a significant part of the reasoning to put Bluegrass into the country classification. Country music's The Grand Ole Opry has featured Bluegrass bands and artists frequently over the years yet country music radio stations seem to shy away from it. Possibly it is due to the pressures that commercialization of music places on the artist.
Commercial music is a business and it is revenue which dictates the sound .
Producers and record companies are not in the business of failure. They have a responsibility to those who finance their operation. The company and their stockholders. This constraint doesn't fit well with a style of music which has such a unique sound. Its risky business to interrupt the flow of Top-40 music with a sound that is basically foreign despite the influence it has had upon the sound.