We think there are two reasons.
First, in terms of sound, Lynyrd Skynyrd was all about guitars. The band was famous for its unusual triple-lead-guitar attack, which pushed far beyond the traditional rock band recipe pioneered in the sixties (one lead guitar) and even beyond the other hard-rocking bands of the seventies (two lead guitars). All those guitars gave Lynyrd Skynyrd a heavy, fuzzy, textured sound—a sound the band showed off to great effect on "Sweet Home Alabama", with the song's signature riff underpinning multiple overlapping solos to create a wall of joyful noise.
Second, in terms of attitude, Lynyrd Skynyrd was all about the South. The band members were genuine southern good ol' boys, proudly carrying the flag for southern culture at a time when the South was being subjected to a huge amount of criticism for its retrograde response to the civil rights movement. "Sweet Home Alabama" instantly became the ultimate anthem of southern pride; it's thus an utterly appropriate calling card for the ultimate southern band.