Anyway, Frankfurt is the next biggest financial center after London, and it tend to get the business when a firm wants to move out of London .
Also from where did you hear that Frankfurt gets the business that's leaving London? What is your source? That was the hope for the Germans with the Brexit, but it never happened. German laws and bureaucracy is still far too hostile and outdated compared to London.
A problem that will solve itself within the next few years
Some even with an American accent which they picked up by watching YouTube videos
https://en.wikipedia.org/wiki/Euronext_Dublin
https://en.wikipedia.org/wiki/London_Stock_Exchange
That said, I'm not entirely clear how the exchange's market cap should or shouldn't be thought of in terms of the total market cap of assets that the exchange lets you trade. Or indeed the float of those assets, which is a concept I've only learned about due to SpaceX's nonsense IPO, so take my thoughts with an appropriate pinch of salt.