They can. There was no dispute that they had sex with the girl, that leaves whether they reasonably believed they had consent. In McDonald's case he and the woman had decided to go into the cab together and head to his hotel room where they had sex. The fact that she was quite visibly very drunk paints him in a poor light but the actions I've listed put doubt on the idea that he couldn't have reasonably believed consent. Evans meanwhile is in a cab with friends on his way home and receieves a text from McDonald that says "got a bird". From that text alone he decides to have the cab driver take him and his mates to McDonald's hotel, lies to the receptionist to get a room key(he'd booked McDonald's room) and then lets himself in to see what he expected, McDonald having sex with a random woman. None of that suggests he is even aware that consent exists as a concept, let alone that he reasonably believes consent was given.
The trial was never seeking to establish whether or not the victim was too drunk to consent. The prosecution establishing her drunkness was simply evidence that the 2 defendants could not have reasonably believed she was consenting. In McDonald's case there is some evidence that she at times seemed a little more sober, although there's also plenty of evidence that also shows the opposite. Maybe Evans recognised her as the girl who had drunkenly fallen over infront of him at the kebab shop, maybe he doesn't, what is clear is that she was very drunk.
This is a great article on the subject, well worth reading:
http://footylaw.co.uk/2015/01/06/ched-evans-sifting-facts-from-fiction/#
Getting in a cab and going to a hotel with somebody doesn't establish consent.
Your own link specifically points out that the prosecution set out to establish that she was too drunk to consent to have sex with Evans, too:
"The only aspect that is in dispute is that Ched Evans says that the victim consented to have sex with him while the prosecution allege that the victim was too drunk to consent."
The judge also pointed out that she was too drunk to consent to have sex in summary:
“CCTV footage shows, in my view, the extent of her intoxication when she stumbled into your friend.”
“As the jury have found, she was in no condition to have sexual intercourse. When you arrived at the hotel you must have realised that.”
McDonald spent considerably more time with the victim, so he must've had a better understanding of her level of intoxication.
If she was too drunk to consent to sex with Evans, then she should definitely have been too drunk to consent to sex with him.
If not, then she was sober enough to consent with both men and she isn't claiming that she turned either man down.
The site that you linked to simply avoids this by saying that the jury could've thought about it differently and avoided the drunkeness aspect.
It's the key part of the case and speaks directly to the inconsistency of the result.
I'm not defending Evans. He clearly acted like a total bellend and I wouldn't have a problem if both men had been convicted.
I could have understood if both men had got off too, as the issue of consent was cloudy, at best.
Letting McDonald off and convicting Evans doesn't add up to me, though.
It'll be interesting to see what caused this conviction to be thrown out, though.
I can't think of what would cause that, apart from maybe something that the victim has said.