> So, something built on the back of the mantra - "centralised services are bad", now needs a centralised custody and holding services because of security? I don't even.
Full disclosure: I'm a "true believer" in cryptocurrencies. I'm a bit disillusioned w/r/t to Bitcoin itself due to community decisions in the past couple of years, but I still firmly believe that cryptocurrencies are here to stay and will grow exponentially for quite some time.
Now that that's out of the way - there's no reason a centralized service couldn't or shouldn't exist atop a decentralized protocol. Decentralization is cryptocurrency's "killer feature", but that doesn't mean that it's appropriate for every use case that it can support or for every user. Indeed, the idea that "your grandma" would understand the intricacies of wallet security - much less m-of-n transactions and smart contracts - has always been laughable.
For a long time, the thing limiting mass adoption was a lack of tools that make Bitcoin and also-rans easy enough for "your grandma" to use. While there is still work to be done in that arena, it's gotten to the point where the limiting factor for the next order of magnitude is network capacity.
Use cases that rely upon centralized solutions alleviate network capacity issues at the expense of control. The things that really make cryptocurrency interesting to me aren't compatible with centralized services, but the rise of those very services will allow the network to grow while we search for a solution to the root problem (capacity). In the meantime, they'll keep the public's interest and continue to ensure that the network is secure and available for those aforementioned interesting use cases.
Coinbase is a great example of this. I really, really don't like the idea of what is effectively a bank having both control of my funds and access to my complete transaction history including metadata that would otherwise not be available to a single entity. Coinbase isn't "interesting" to me, but it is useful. I'm happy to use it to move a small amount of USD to cryptocurrencies and make small, trivial transactions. There's nothing at all wrong with using it that way, and it supports merchant adoption to boot.