I can't get inside any of Mark, Tom, or Travis' head but in retrospect my gut says Tom was just done with blink after the whole Boxcar dilemna, he was changing, he realized Mark and him would never be close again but he still had a little heart left for something that was so much a part of him for so long and gave it his one last all on Untitled, sort of like his love letter to blink 182. Tom might be crazy, but he is pretty true to him self artistically, while Mark was always about the success, fortune, and fame experience. Tom moved on, possibly not being financially aware of the difficulty of 'keeping' wealth versus making all that money at once. Tom's ego got a little carried away but he couldn't go back, damage was done. Neighborhoods, while it did age greatly, was clearly Tom at a bit rock bottom needing help, more than likely financially. He 100% used the easiest answer to force a reunion he didn't want to do with blink. The body language showed he could never fully commit back to it as it was in the past to him. He, still being an effortless songwriter that he is, helped make a decent but offbeat album. It was a bit underwhelming, even Up All Night to me, partly because it was so confusing at the time what was going on. Many of us were young-ish still and were expecting a fairy tale story line of this happy exciting reunion, not understanding the truth of it really. It still had blink elements, so I enjoyed the fuck out of it while I could, and listened to DED a lot too (I think Tom matured a bit here and realized how much blink gave him and how douchey he was sort of getting and made something more modest). Being such an outcast album, it has a bit of a charm to it now and really did age well now that many of us have accepted this is how life goes a lot of the time and is never storybook like you see things growing up. California obviously helping it age even better being such a contrast to everything that album is.
Mark, being completely bitter and broken had to find a way to move on and went on to what would be a great marketing grab, a new band that clearly has some songs focused on the breakup of blink and his anger towards Tom. We have to remember, blink was MASSIVE back in the day, everyone was eager to see what they did next and +44 had a chance with some more elements, Mark just gave up real quick. Mark probably held out a 10% chance Tom actually cared with Neighborhoods, he knew how painful that would be if he was fooled after such a long hiatus. He didn't really want to admit it at first, but clearly was frustrated and angry during the tours. The Neighborhoods album he was really off, just could not move on from the glory days (for him) in Dammit, Enema and Toypaj. Mark was always a college guy at heart, he hated the idea of maturity that Tom wanted. I do think he's found more inner peace, but musically the guy is pretty lost and all over the place trying to make decisions, guitar skills didn't fade though. He needs Tom's crazy and lack of hesitation to balance him out.
Travis was just along for the ride.
Bolded the actual answer to quote part. Not being pretentious, just don't know why I wrote a book.