Hey, so uh, I am just going to assume you're quite young OP. And I don't mean that in a judgemental way, at all. But I do feel the need to chime in here.
Just because your personal approach to dating is just trying to exclusively reach the "end goal" of marriage.... That doesn't mean everyone else in the world feels the same. Like, you understand that, right? In the real world, LOTS of people do not enter into a relationship with the thought "I better be married by our 2 year anniversary!". Again, I am not taking a dig at you.
I'm just saying, your ideals and expectations about your romantic relationships aren't the end-all, be-all, of how ALL relationships "should" be.
In the same way that sexuality and gender are fluid spectrums, peoples' approaches to their romantic and/or sexual relationships can also be a vast and fluid spectrum.
Penelope is a fictional character. And as someone who has been watching this show since it first aired, I fully believe her decision to choose her career and her BAU family, over marrying Kevin and moving away so she could fulfil his narrow perception of what a relationship "should be" - was 10000%%% in-line with everything we knew about Garcia at the time, AND everything we know about her now!!
JJ never wanted to marry Will, even when they'd been together for years and had a son together. Was she "wrong" for that? Yes, they ultimately got married, but not before SHE was absolutely ready for that commitment.
Tara walked away from her first marriage, because Darryl's drug use was detrimental to Tara's mental and emotional well-being. Do you think she was wrong for leaving, just because it broke Darryl's heart? What about her relationship with Doug? They were engaged. Like Kevin, he demanded that Tara make him her #1 priority, instead of all the time and focus she was spending on her career. When they broke up because she chose her career, was she being selfish?
If your answer is no to any of the above questions, then PLEASE ask yourself why it's Penelope you're blaming here.
Penelope is canonically having casual sex with multiple partners in the current season. Does that make her less-likable to you? In your opinion, is she 'doing these people wrong' because she's not planning on marrying them??
She's a 50+ year old woman, who has casual hook-ups to fulfil her sexual needs, while she receives all of her emotional needs for happiness, love, stability, and comfort, from her platonic friendships. Who cares if she doesn't want to get married?!? She's happy, she's thriving, she's living her truth.
Now, I'm not going to assume your sexual and/or romantic identity OP, but I would remiss if I didn't point out the obvious here. In real life, if someone prefers to invest in their deep, meaningful, loyal friendships — rather than focusing their entire life on a romantic partner/spouse —like Penelope does, well, that person might ID as being on the aromantic spectrum.
By dissing Penelope for not wanting to marry Kevin, merely because it was "expected" of her within any long-term relationship, whether you mean to or not, you are perpetuating ideals that contribute to real-world aromantic oppression.
And considering Aro people are part of the queer community, you're also perpetuating queer oppression, in general.
During pride month, no less.
I'm not saying you're not allowed to have your own headcanons and opinions about fictional media. But I really, really, implore you to step back and think about what sort of real-world prejudices you are applying to those opinions, and what kind of real-world harm your posts might cause other fans who come across them.