Blame the executives at UA
They kept pouring more and more money into a movie with a genre that wasn't profitable, with actors that had no box-office potential, and with a script that had no real narrative through-line.
If their money meant so much to them, alarm bells should've been ringing before the first budget had even been set. But the fact is they kept pushing ahead with it, throwing more and more money at Cimino, because they thought the guy was the goose that laid the golden egg. They wanted another Deer Hunter and were content to let Cimino do whatever he wanted until it no longer suited their purposes.
If the execs had any clue what they were doing, the screenplay would never have been green lit without an actual star in the lead role. A $4 mill western with Clint Eastwood = guarenteed blockbuster. An $11 mill western (eventually $40 million) with Kristofferson? Forget it. It was simply bad management.