United Kingdom 450 is a count not because the UK actually launches so many satellites of its own, but rather because legacy commercial telecom operators (geostationary like INMARSAT and others) are often UK incorporated. Dig deep enough into commercial satellite telecom and you'll find stuff with offices in the City of London.

Why did many telecom companies put their offices in the City of London?

Taxes, US regulation, military shenanigans?

Finances and investment... not so much that their corporate HQ is legally in the city of london specifically but the people arranging debt/financing to do big costly telecom projects will be adjacent to the NYC and/or London financial markets. Same reason why a lot of submarine telecom projects are closely linked to things in London. If you need to spend a ridiculous amount of money for something that has a 10, 15+ year ROI you need a massive amount of debt and that money can only come from a few sources in the English-speaking world.

Yep, they should be.