It's simple. A ton of men are sick of being used and taken for granted by entitled women. This story is ultimately a woman's fantasy about using a man and taking his kindness and support for granted and it being cast in an acceptable light. If you look past the bright coat of paint, it's the story of a woman being allowed to do something unforgivably hurtful, and the man she hurt still loves her and picks up the pieces for her anyway after 17 years of being apart. It is viscerally disgusting to see this sort of unhealthy premise presented as "cozy" when in reality it's nightmarish.
Sure, this is a story that could reasonably happen in reality... but in reality, she's a parasite, and he's pathetic for clinging on to her memory and taking her back in when, from all indications, she abandoned him. She went off and gave the greatest singular gift she could give to another man by bearing his child. Meanwhile, rather than moving on, this schmuck carried his feelings for her for 17 years, to the extent that the instant she showed back up at his doorstep needing his help after vanishing from his life, he immediately provided her and her bratty bastard child a home with no expectations. Not even an explanation. There's no accountability for what she did whatsoever. This idiot is the perfect wish-fulfillment to a woman trying to escape from the consequences of her selfish, stupid, heartless actions and the harm they've caused.
And none of this is truly acknowledged by the story. All of the dilemmas implied by the premise are essentially ignored and put off, disconnected from the emotional throughway of the narrative. How convenient for all of this to be swept under the rug.
The idea far too closely mirrors scenarios where women leave good men they're in stable relationships with for some shitty tenuous reason like they're "bored," or they think they've missed out on something, or they've found another man they think they'll get a better deal with, only to come crawling back begging to be given another chance in the end when their selfish, stupid, heartless decisions blow up in their faces and they realize the grass was greenest on the side they left behind. It doesn't matter if the premise is explained away as something entirely different and justified down the line, because at that point you can be sure it's going to be some contrived nonsense.