While there is nothing inherently wrong with storylines about lesbian mothers, on screen portrayals suffer from both the execution (the trope is often linked to the Desexualized trope, the Lesbian Sleeps with a Man trope or Rape/Sexual Assault) and its widespread presence.
In 2003, Sarah Warn, then editor of AfterEllen.com stated:
“The number of lesbian characters on TV whose storylines revolve around their role as a mother (or desire to be a mother) has grown to such epidemic proportions, it now appears that all lesbians do is have and raise children — when they’re not losing custody of them and fighting to get them back.
Another popular plot device in recent years is to make the mother of a main character gay, such as Roseanne’s mother on Roseanne (1996), Steve’s mother on Beverly Hills 90210 (1999), Harrison’s mother on Popular (1999) or Raina’s mothers (played by Sally Struthers and Debbie Allen) on The Division.
It isn’t even that so many of the lesbian characters are mothers that is the problem — it’s that their storylines revolve around their role as a mother as if it defined them exclusively.
Trying to conceive, adopt, get custody, or otherwise deal with children are virtually the only stories adult lesbians get on TV anymore (besides coming out), and the reason TV writers fall back on this storyline is less about exploring the joys of motherhood than it is about desexualizing lesbians and making them more palatable for straight viewers.”
Although there are more lesbian and bisexual characters today, the prevalence of the Bury Your Gays or Drive-by Lesbian tropes still leaves lesbians-as-mothers as one of the more common portrayals, in cases when the characters get to live or remain on the show.