Cool stuff, most banks, brokers and hedge funds have no FOSS culture.

That said, the major blockers for financial services, at least in my country, are sort of unrelated to open source software being available.

Thinking about the most basic questions one needs to answer to start a fintech:

1. I want to create a bank. How do I do that?

2. I want to issue credit cards / lend money / make a payment system. How do I do that?

3. I want to start an investment fund. How do I do that?

Those are just some examples, but each one of those questions lead to infinite rabbit holes of laws, regulations, bizarre costs and arcane systems to integrate to.

I have more experience with (3) and stuff like getting reliable market data, connecting to brokers and exchanges, sticking with compliance rules, etc... are easily the most painful and costly bits of my job.