I didn't read the books, this is show-based.
From what I remember of the first two seasons, Penelope has been unfortunate enough to have been raised by shitty parents. Her Father, a gambler who abandoned her and her family. But most importantly, Penelope's mother; a woman who does not accept or support her daughter. Her mother has done nothing but poison Pen with insecurities her entire life; the most obvious being blatant emotional neglect. Specifically the nitpicking, criticism, comparison to her sisters, training her to reject her own thoughts and worry so much about what people think that Pen lacks basic social skills, and then her mother is constantly nagging her to stop reading books which are one of Pen's only escapes. And more!
After a lifetime of that, I think Pen seemed to feel that nobody could possibly ever love her. Her parents didn't, her sisters don't, and no man did. Obvious lack of self esteem not only for her looks but who she was as a person right down to her core. The type of damage that a narcissistic abuser does.
For a while Pen was hanging out with Eloise and her anti-marriage, anti-man, free woman ideals. Not criticizing those ideals by the way, but in Pen's case, these ideals didn't always line up with who Pen is at her core. I think it's entirely possible that some of those ideals were a resignation to her (false) feelings that she was not worthy of love. Those ideals helped her cope, perhaps.
Meanwhile, Pen spends her time reading an awful lot of romance novels and referred to them as "hope" for a better life. This implies that she is first off, miserable, and in a lot of pain, and is deeply longing for a passionate, loving relationship. This idea doesn't just apply to a husband though. I think she longs for a family that accepts her and loves her too.
In S3, it was Debling who pointed out that Pen stares out the window not because she "likes the view" but because that's where her true love lives. He's not wrong. But I do think it's the view; it's the whole entire view - the Bridgertons. I think Pen wishes she had a family like that. A loving and supportive family, whose matriarch married for love, whose children are encouraged to marry for love, Colin is also there, oh and her BFF is there - who she does miss a lot.
Also meanwhile, Pen is quite literally writing a true romance novel of her own every week by following what seems like town gossip but is essentially, stories about love and relationships and how they are formed. She's literally a scholar of love and human behavior at this point, as she seems to be fascinated by all of it. Not only does she read it, but she observes it, studies it, analyzes it, and writes reports! And in doing so, she became the Ton's favorite writer. No wonder she loves writing! She's constantly validated by everyone in town and knows that people accept and appreciate her even though they don't know who she is. Edit: after discussing with these fine redditors, I want to add that she uses LW writings as a means of standing up to the bullying she's received by throwing it back at them in a very publicly humiliating way and it's arguable that this is wrong. It's also arguable that it's so very right depending on your moral compass.
TLDR; Anyway to the point. Pen is a victim of emotional abuse and neglect, who longs to be accepted and loved by not only a man, but a family. She's not a shallow person because of what she writes, she just desperately wants to be surrounded by love in every way possible and wants to also share it with everyone Edit: She also wants people to be kind and has the capacity to fight those who aren't using their own methods, but she's trying to teach kindness and love.
Which brings me to my last point, the inspiration for me writing this post, regarding a comment I made about why Pen and Debling would be an AWFUL match.
A marriage to Debling would be nothing more than a continuation of her life at home. Staring out the window of a prison, with her romance novels, longing to be loved by a husband who's never home. Which would just be the same familiar cold neglect that she's been experiencing her whole life.