Probably a multifaceted reason, but I think some parts are the universality of her lyrical themes of heartbreak and loss of love, and finding new love and the hope it brings – which I feel she can now wrap in multiple layers of cryptology and her fans would still deduce who and what the lyrics are referencing (and I think a part of fans love doing this). Plus her music is easy listening, ranging from country to pop. Also there is sense of female empowerement from her struggle to acquire the rights to her own works.