Because they are bad urban fantasy novels... only without the bad part. They're written by a husband-wife team (Ilona and Andrews is a portmanteau of their names) so the romance, instead of being high on the long looks and bodice ripping, is high on snarky interplay and the two characters actually building a relationship and their weird world.
If the shapeshifters/magic/post magical apocalypse setting turns you off then I say don't go any further, but if you can take magic and fairies and stuff, then it's the best. Magic Bites is where to start, name pun with the werelion fully intended. Eh, you know what, I'll just borrow from the first Amazon review:
>It was and is a treasure. I love Kate. I love Curran. And Julie. And Derek, and Jim, and Mahon, and Roman (his PJs game is ELITE), and Ghastek, and, well... all of them. My husband and I talk smack while we listen to what the various characters say. We tried to kill Hugh like, I don't know, five times for any number the things he's done in Roland's name. But that is what makes this series so good! We GET these characters, and we can geek out about them because they act like people we know (I'm personally convinced that members of my family are part of Clan Wolf (which ones and why are for me alone)).
It's just fucking hilarious. Also I'm pretty sure they had like no input on the covers for their novels, their newer works tend to have more fanciful/silly stuff.
I'll tell you how I liked the Three Body problem when I finally get to it, but I admit it is kind of last on my list (also The Fifth Season begins with "Let's start with the end of the world, why don't we? Get it over with and move on to more interesting things" so that's just begging to be top of the list)
Memories of the Fallhas gained 60,000 views since I last checked, but is still sub-200k. An excellent Xianxia novel by an Irish author, it brings in elements of Eldritch horror, alternate worlds, and strong horror influences along with a very non-standard storyline.
So lets get more obscure. Kill Kill Kill requires you to have a sick sense of humor and a strong stomach. A VERY sick sense of humor. Yet I would argue it's absolutely a progression fantasy, albeit an unconventional one. Book one deals with the lizard people (who absolutely run the world). If you enjoy it, check out the followup adventures of Kill Team One, as it more closely follows Sid (the least awful person in the book) and deals with Werewolves, his brother (the most awful person in the book), an undead ghoul, a Communist nanoswarm, and Chinese mystics. This is insanity.
Urban fantasy often has an amazing amount in common with progression fantasy. And of them, Magic Bites starts off my favorite series. Following a swordswoman with quite a bit of magic as she grows into a powerhouse in her own right, fighting Celtic and Egyptian Gods, Hindu myths, and an ancient Babylonian blood sorcerer (just don't call him a God. He doesn't want to be limited that way). Oh and vampires are distinctly NOT sexy (or sentient). Popular, but probably not a popular recommendation on this forum.
Fates Parallel is a coming-of-age/Xianxia story with good progression and some nice twists, and a fairly slow burn romance subplot. It never overshadows the main plot, but it's a very important element of the books, as is progression.
Magic Bites is not as free, and the main character starts older (early 20s) but there's a strong progression element and romance throughout the series, and the humor is on point. As is the action. One of my favorite series of all time.