The fact that they couldn’t bother to tell how the two even broke up in the first place, why Marceline would let her cherished loved one be kidnapped repeatedly over possibly decades, ignoring PB’s dedication to her citizens and duty as princess (hence why she’s always out of the kingdom during any bubbline moments ex: Varmints, Broke His Crown, Stakes, What Was Missing.) Marceline hates regal shit. There’s no way to have her in a throne room because she isn’t that kind of gal.
How about that PB age retcon to satisfy its shippers when there’s canon evidence of her just being a mortal royal daughter?
How about the need to nuke any most aspects of their original personalities in order to make them cozy up to one another. Can’t have Finn near them or acting competently so you have to throw the entire garbage maturity arc at him. What was left of Marceline after S4? Muh feels, Bubbline and Simon. God knows why the pandering rock shirt had more value than Huambo (after I Remember You) and PB’s sniffing a shirt after ridiculing Finn about the gum hair thing and her still reeling from Too Young and Burning Low.