It's stretching it to say the issues were insurmountable for the A380 gates, it's more of a cost benefit analysis.
GLA added infrastructure to a 1994 build pier.
MAN added infrastructure to a 1960s build pier.
LGW added the infrastructure to a 1988 build pier.
If they'd wanted to add an A380 gate, then down the end of the new Pier 1 would have been relatively straightforward, if not a little more expensive on a 2020 new build. But if the plan was to add them onto the next phase then it's all fair IMHO.