Yes, it has to do with promoters but also with Dylan (or, at least, with his touring management) and the fee he seeks and the profit the promoter and the venue wish to make. As it happens, most of Dylan's European tours are co-ordinated through a UK promoter who commonly uses local promoters in each country to set up things there, so there can be two lots of promoters to satisfy, financially. They, of course, have to assess Dylan's likely ticket sales and the prices that might be charged (taking account of his popularity, how long since his last visit, how well he did last time, where the other cities are on the tour, how favourable recent media coverage has been, and so on and so on) and then have to balance that against what the venues want. Dylan's small venue date in Stockholm was added after the tour had been set up, so the basic economics of the tour had essentially been worked out already.
As for Mark appearing on Dylan's 1973 "DYLAN" album, I think not. That album was issued by Columbia Records after Dylan had moved to Asylum Records. Columbia used material recorded in 1970.
