Why are there separate packages for pluggable-transport versions of TBB? Seeing as how anonymity is the point of Tor, why wouldn't traffic be camouflaged by default? Especially since various governments and agencies give it extra attention.
To connect using Pluggable Transports as a client, you need to know about at least one bridge relay that offers this particular pluggable transport. This list of bridges is not public, because that would make them trivial to block - directly working against the point of having bridges in the first place.
If you connect to the Tor network directly, you don't need any special knowledge. Your Tor client can query the publicly available directory servers and learn about all the Tor relays there are and connect and use the Tor network.
The anonymity comes from using the public Tor network to build your connections. Pluggable transports don't provide anonymity - their goal is to allow you to connect to the Tor cloud in the first place in case you are in a location that filters your Internet.