Add to the fact that people are also DDOS websites (doesn't take a "big money institution" to do that) and it seems the explanation is clear...
I'm much more inclined to believe the downtime is caused by scaling issues rather than some big conspiracy,
EDIT: Just to give some insight, one of the problems we run into is that usually only one issue is exposed during an outage. For example, lets say we have 10 functions (or services or whatever) in a row that all call each other. All the odd numbered ones have issues where they fail at scale. During the first downtime, function one will fail and start to throw errors, but this means the full traffic load isn't reaching the rest of the functions. By the time the problem is solved, traffic has usually died down, so function 1 is fixed, but 3,5,7,9 still have issues that haven't been exposed.
Additionally, at a quickly growing company like Coinbase, the code isn't going to stay the same for very long, so even once those functions are fixed, new issues are introduced.
It's easy to say they should be load testing at 10x their expected load to prevent these type of issues, but it's really hard to replicate production traffic. Users do weird and unexpected shit that can cause problems.
It's funny how quickly people jump to overly-complex or borderline conspiratorial explanations when the obvious is staring us in the face...
Coinbase might be a large well funded organization but it's still run by developers with giant backlogs of tickets and conflicting priorities to build new stuff vs maintain old stuff.
This times 1,000.
So yeah, I find these weird circuit breaker patterns suspicious. The worst part is "partial" degradation, when you can't execute trades, but someone else can. It's very easy to hide all sorts of irregularities behind these partial outages.
I'm sure they would pay you a lot of money to solve their scaling issues, if you were so inclined.