There are a couple reasons why it's really difficult to disrupt this industry:
1) An mvp won't cut it. If I'm a trader with 300MM in my pocket, then I need access to information. All information.
2)Reliability. Traders need a highly reliable connection. No room for error. A great counter example is Reuters. I worked on a support desk where I had both Reuters and Bloomberg (at a cost of something insane, probably close to 100k/yr). I imagine that when a major pricing error occurred on any exchange, I would find out within 30 seconds to a minute. Despite all its resources, Reuters proved time and again to have pricing issues. Connecting to hundreds of exchanges with thousands of securities is difficult. When you start to go outside of the US, there's some really bizarre logic. Bloomberg was incredibly reliable on the other hand, and their support team responds to issues within minutes.
2) Network effects. Bloomberg messenger is the way to communicate in finance. Also, Bloomberg leverages its network to constantly monitor prices, so pricing problems are discovered REALLY quickly. It's kind of like open-sourcing security pricing monitoring.
3) Reputation. Even if you create a perfect replica of Bloomberg, would I stake my clients money on your track record? Even with a good track record, why would I not trust Bloomberg when it's the de facto standard?
4) IP? not sure about this one, but I imagine there are a lot of features baked into Bloomberg with legal protection.
5) The cost is insignificant for most of wall street.
Funny story: on a whim I interviewed with capital IQ while I was in college. They asked me to design an interface that would allow people to access financial information quickly. Having never used or seen Bloomberg, I immediately started describing a system of keyboard shortcuts, to which my interviewer responded that I was basically just describing Bloomberg terminal. Didn't get the job.