Can't be the only one who is tired of a lot of manga having very unsatisfying endings after long runs. Food Wars ending was fucking ridiculous. Turned it into a pseudo romance plot, but nothing happened. That's alright, he will release a monthly 3 part epilogue series...which confirms the weird incest plot, and does nothing with the romance plot at all. Didn't resolve shit.Honestly, it wouldn't be surprising. A LOT of manga authors purposefully tank their series when publishers intervene. A notable example is Food Wars. There was apparently publisher interference, so he purposefully made a dude with super powers, brainwashing, this weird incest plot and a completely, utterly trash ending hated by all.
Another instance of interference was High School DxD. The reason why the MC never gets laid even though everyone wants to fuck him is because the publisher basically vetoed any fucking and kept it as pure Ecchi. He didn't drive the series into the ground, but since there was no sexy times, he basically ditches the ecchi stuff later on and it basically becomes another shonen title. It was kind of absurd.
So it DOES make sense that if Isayama wanted to do a different manga, but his publisher was adamant about AoT, he just went 'fuck you' and tanked it out of spite, since he knew it would sell.
Bleach also had an unsatisfying ending. Used to be one of the "Big 3 of Shounen", ends with two deus ex machinas in order to defeat this OP villain. One to repair Ichigo's Bankai, another to give Yhwach a moment of weakness from this "tainted arrow" that we never heard of before. Ended up having to write a few light novels to clear up some details, which if you never followed up on, would leave the state of the world a complete mess.
Worst one I saw was "Gal Clean", one of these gal mangas which got the axe early. Author then turned it from a happy go fun loving manga to a literal rape plot with the words "the cleaning never ends" as a "fuck you" ending to the editor.
As for Attack on Titan. I don't even know where this is going or how this is going to end. This shit lost me some time ago, and I'm not looking forward to the ending of this.