I've certainly heard about MongoDB many, many times. I've heard of Redis some. I've heard of CouchDB. But this is the very first time I've ever heard of "Couchbase".
Compared to a closer example like RethinkDB, which was really cool, but nowhere near the money and marketing team ultimately failed. Rethink started in terms of stable data first, performance tuning from there... mongo went the opposite approach and caught up on the stability later. Of course scaling mongo and administration isn't as easy as a single node, or multiple read-replicas.
Because MongoDB is a single binary to download and install and has one of the simplest config files around.
It's arguably the easiest database to use and operate.
If you're looking for a super low-latency (everything sub-millisecond) document/json store with strong resiliency options, cross-data centre replication, options for optimistic/pessimistic locking, json sub document access and modification, etc etc, I don't know why you'd use anything else.
It really depends on your specific environment in terms of how much you are, or are not willing to lose information and it's all relative. I'm a fan of high performing databases (couchbase), or those more tunable (ScyllaDB/Cassandra), or build for indexing (elasticsearch), or those built for consistency (sql).
Each have their use cases, and there's definitely overlap. Understanding the difference and using the right tool for the job is important.
Edit: typos