Again, look at the competition. Is it any easier for other cities?
- London: higher salaries, much higher CoL => lower disposable income
- Dublin: barely higher salaries, higher CoL
- Amsterdam: similar/lower salaries, higher CoL
- Paris: lower salaries, higher CoL
- Stockholm, Helsinki: lower salaries, higher CoL (and crazy housing situation in Stockholm)
- Southern/Eastern Europe, Baltics: low CoL but the salaries are bad
You want to make good money? This leaves Oslo and Copenhagen where your overall purchasing power isn't going to be that much higher. The true outliers are Luxembourg and Switzerland where the tech ecosystem sadly isn't very exciting (why do you think a Swiss would take a job in Berlin? :)
I don't think Europe will ever be able to create a tech hub similar to the SV. And without a high concentration of talent, salaries can't go that much higher. London might get somewhere closer to NYC, but right now there's a very significant gap between finance and the rest. And Brexit will certainly not help.