The distinction you're missing is between economic activity and wealth retention. Foreign investment in UK data centres generates GDP (construction jobs, some ops roles) but the productive capital and its returns accrue to foreign shareholders. This is the classic GDP vs GNI gap - Ireland is the textbook example, enormous GDP inflated by multinationals, but GNI per capita significantly lower because profits repatriate.
If a fund invests £100bn expecting 15-20% IRR, they're extracting multiples of that over the asset lifetime. That's the whole point - they're not philanthropists. The UK tax take is thin because these structures are explicitly designed for tax efficiency.
The deeper issue is where in the value chain the UK is positioning itself. Hosting someone else's compute is the low-margin end - it's being a warehouse. The high-margin positions are fabrication and supply chain. Taiwan, South Korea, and now the US via CHIPS Act understand this. They're not inviting hyperscalers to build data centres and calling it industrial strategy - they're building domestic fab capacity because that's where durable value and strategic leverage sit.
The UK is offering itself as a site rather than building itself as a participant. Those are very different things.