One of the main reasons that "IT" and developers specifically choose the UK or more specifically London it's that it's the only place where you can get salaries which are even remotely close to what you get in the US. A developer in spain earns about 35K Euro's, a developer in Berlin earns 60K. Deserving or not IT doesn't pay more than most professional positions in the EU and in many places you would be getting paid about as much as some public sector workers and teachers. While the average UK developer salary isn't considerably higher than Germany, the London salaries are considerably higher and it is the only tech hub where developers can break the 100K GBP(~130K US in the current market, but it was 150K+ just a year ago) mark in Europe.

Add to that the fact that non-base compensation is very low in Europe in general, bonuses are fairly low, equity is considerably rarer than in the US, large tech companies would give you access to some sort of an employee investment plan but that's about it the UK was and still is pretty important in keeping IT talent within the EU. Given the usual risk averse culture of most of the continental states (with somewhat the exception of Eastern europe and the baltic states) it's quite unlikely that a true startup hub can emerge anywhere else, the UK or again more specifically London had access to a lot of financial capital which helped it to compensate for the usual European aversion from risk, venture capital and the startup culture in general.