It's all of the above. There was huge pressure from Atlantic to get the next album out. Part of that was because Wakeman's keyboards were very expensive. I've never seen it spelled out explicitly, but I've always taken that to mean that the label actually bought the equipment and wanted their investment back. It seems weird that the label would buy the equipment in the first place, but the Wakeman deal was weird all the way around. Maybe it was Wakeman personally who went deep into debt? That doesn't make much sense, either, but who knows?
The liner notes talk about how there are spotlight tracks for each of the band members. The Fish is Squire, Mood for a Day is obviously Howe, Five Per Cent for Nothing is Bruford, and We Have Heaven is Anderson. Wakeman had a piece ready, but he was contracted to A&M records, and the terms of him appearing on Atlantic forbade him from recording any original music with them. So at the last minute, he whipped up "Cans and Brahms". I personally like it. In the 70's, it was still pretty novel to arrange a classical piece entirely for keyboards, and the idea of each section being played on a different keyboard seemed pretty cool to me. I think I was still in junior high when Fragile came out. I remember my mom had to drive me to the store to get it.
The five solo tracks were literally filler, because the band only had four songs ready and the label was pressuring them to get the next album out because they have bills to pay. It was presented as a way to spotlight each of the members, but it was really because Yes take a long time to write and record songs, but the solo tracks could be put together relatively quickly.
Anyway, I referred to Can and Brahms as "weak" because on the Yesfans boards, it seems to be considered pretty bad. At least part of that is because the piece Wakeman had prepared became Catherine of Aragon from his solo album The Six Wives of Henry VIII, and it's one of the standout tracks.