Adding my 2 euro cents (about 2.5 US cents, or 1.7p, or about 70 kopeks) worth:
Yes they went too early in the season - June is not the time to be in that part of the world ... but thats not the reason they didnt make it. They were smart enough to hook up with Rayil Zalyalov (the then head of the 4WD club in Yakutsk) who famously told them in the video when they asked if they can make it unaided at that time of year "I think no" ... which proved to be a spot on assessment. So the LWR team countered the wrong time of year factor by getting Rayil to accompany them all the way to Magadan, and getting Rayil to arrange several trucks to accompany them on the Old Summer Road section. That way water levels were not really a factor ... anything too deep saw them put the bikes on Rayil's trucks.
Clearly the bikes were too big and too heavy. This obviously became a factor. Ostensibly Charlie hurt his back halfway along the road and so they put the bikes on the trucks for the hardest part ... the eastern end of the Old Summer Road.
Personally, I dont buy it. I suspect the road was getting tougher and tougher and with the heavy bikes became a real chore. The tendency when you have an easy way out (trucks with you) and the going is tough is that you mentally crack and say 'fu@k it, stick them on the trucks.'
Charlie's back was suddenly better exactly when the hard road finished and they unloaded the bikes to ride the main highway into Magadan.
The advantage we had, (apart from more suitable bikes) was that there was no support trucks, so there was no easy way out. Mentally there is only one option ... to go on.
I certainly dont think it was better riding talent. Charlie is by all accounts a very capable rider, and Ewan had a lot more training than Sherri Jo, not to mention thousands of miles of dirtroad experience by that stage.
I often advise peoplу that the number one piece of prep you need for a tough ride, is mental ... forget riding talent, even experience you can discount. As for bikes, you can go round the world on any bike. But there is no substitute for a 'no quit' mentality. You have to be determined that nothing will stop you for the end goal, and focus only on defeating the obstacle ahead of you. If you start to think of easy ways out, then inevitably, you will use them. They needed the trucks with them because they were there too early in the year, but having the trucks with them made it too tempting ... they got tempted!