>>57707964For Kekkai Sensen its because they went more faithful to the manga. A good chunk of KS's first season was anime original (basically everything involving black and white) while it picked specific chapters to adapt out of order to keep the ongoing story more tightly focused. S2 was more faithful to the manga, with the plot kind of all over the place and jumping from character to character before the finale that was a multi-chapter story from the manga which is why it felt like there was so little buildup. Basically KS was best when they added more original material to it to link the various chapters together and give it a sense of story progress.
DtB has no second season.
It fell apart in its second season because it basically abandoned everything the first season built up in favor of focusing on a dull as fuck new character and her borimg twin plotline with the magic mystery meteor. Electric batman? Sorry, Hei lost his powers and is now an abusive drunk who spends most of the series moping. Yin? Sorry, she's kidnapped all season and is suddenly super powerful and important which is only explained in an OVA released after the series ends. The individual story arcs that gave you action while world building and forming and ongoing plot in the background? Nah, we're going to have minimal action and a lot more talking about vague crap only loosely related to the plot or what's happening while pretending the plot is progressing. Also the resolution to the plot is terrible and added nothing to worldbuilding or understanding of what was going on with the stuff happening to the setting like the first series did, and instead it felt like a pointless sidequest and no payoff. Basically they diverted too heavily in content from the first series and it comes across as almost an entirely different series with some familiar names and terms slapped onto it. I will forever remain salty that they ruined this series as hard as they did. 