A brand new depot would have a design life of 50+ years. Materials costing more simply doesn't cut it as a believable reason why they have chosen not to replace like for like. A far more plausible reason is that they genuinely don't foresee a return to pre-Covid revenues, and they have also looked at the politics of this country and the geopolitics of electric vehicle production, and concluded that, for the next few years at least, only a lunatic would make an investment of this type.