London provides enormous amounts of financial services to Europe. Around 35% of all wholesale financial activity in Europe takes place in London. Around 85% of European hedge funds are there. Around 44% of all worldwide euro trading takes place there and around 70% of all derivatives trading. Figures from https://www.thecityuk.com/assets/2016/Reports-PDF/The-UK-Eur...
In other words European companies rely heavily on people who currently live in London and presumably are settled there.
In any normal situation this would be seen as "The EU wants access to London based services, we'd better make sure we negotiate that!". However that isn't what is happening. Instead the EU plans to simply pass new laws (changing the MiFiD II rules that aren't even implemented yet) in order to force the people who live in London to sell their homes, pull their children out of school, learn new languages and move elsewhere. The banking industry is resigned to this fate and barely even comments on it.
To me this is indicative of the terrifying fanaticism at the heart of the EU. Talking about it is one of the taboos that Brexit has started to break. The people who run the EU are utterly, utterly unconcerned about the lives of the people who work in finance, they're utterly unconcerned about the economic welfare of European companies that heavily rely on the UK for financial services, they've refused to take up Theresa May's offer of ruling out forced expulsions right at the start, and their "plan" appears to be to refuse to negotiate any kind of cooperation at all until after the two year exit period is up.
This is not what responsible, mature leadership looks like. This is what it looks like when people get it in their heads that they can do anything and nobody can stop them. You can always tell when there's a true fanatic in the room because the reasonable people start blaming each other for the "inevitable" consequences of trying to defy the fanatics. Their unbending will regardless of the cost comes to be seen as a fact of life that just has to be accepted, and everyone else starts to work around them and even blaming themselves for it.
Europe will become a healthier place when people in positions of power and respect start being able to say that the EU is run by fanatics.