Only the original series aired on PBS. The 1998 and 2001 series were both on Showtime.
The Hollywood Reporter tells why the followups were not on PBS:
Despite record ratings and a Peabody Award, PBS dropped the show under pressure from a campaign led by Maupin's old boss, by then Senator Jesse Helms, who fulminated over the use of taxpayer dollars to fund what he branded as depravity. The 12-minute montage screened in the Senate stitched together just about every moment of sex, drugs, nudity and profanity from the first series; it looks amusingly mild in hindsight, compared to the far racier content that now gets aired even on basic cable. "We made a beautiful show about family, and everyone's right to search for love," says producer Alan Poul of the series, subsequent seasons of which aired on Showtime.