They had a really terrible tour in the Northwest where they had a bunch of broken equipment, a broken tour van, and had to borrow money from friends/family back home just to ensure they could finish the tour. They also had a bunch of personal drama back home. They also were sort of inspired by the early days of Modest Mouse, who basically traveled the country in a beat up van and played dive bars for years before they commercially broke through, and they realized that romanticized idea was much more miserable in practice. Deakin also mentioned that the four of them were not getting along on that tour, and Geo mentioned that they "needed space". So there was a lot of incentive to kind of take some time away from each other at the end of the HCTI recording process.

No one's really sure why Panda stuck around, because touring was always the hardest on him because he has always had extreme anxiety in regards to being on the road/touring.

Geo went to grad school at the end of the HCTI process. He had been accepted prior to beginning the tour, but after such a terrible experience, he basically accepted his admission offer in the middle of the tour. Deakin left and became a carpenter for a while and was working full time doing that during ST.

Avey has mentioned that the lyrics on Sung Tongs were the first time that he started to write lyrics from his own perspective, rather than just generalized stories, and a lot of the ST songs came about as the HCTI era came to an end and the ST era started, so it makes sense that those then-recent experiences were what shaped the lyrical content of ST.

It's kind of important to note though that Avey is actually the person that never has talked much about "negative" touring experiences, he even enjoyed playing to essentially no-one during the Danse tour with Black Dice. So while I think that Panda/Deakin/Geo all had their own problems that sort of came to a head on that HCTI tour, Avey never really indicated that he had as bad of a time as everyone else did on that tour, so I'm not really sure that anything on ST (which was almost entirely written by Avey except Leaf House) really captures the feeling of that tour to the rest of Animal Collective.