At some point large projects can be difficult to manage, so there is a synergy that typically needs to be established between scripting assets. For instance using a portal asset and interacting with it via Playmaker would probably be the easiest path. Creating a portal system with nothing more than Playmaker would likely be counterproductive because of the time it would take to create the system.
Of course, a simple teleporting thing is really easy but something very robust like how Valve's Portal game handles things is absolutely not a good idea to create in Playmaker alone. There is some very complex stuff going on in there and its just way easier to handle those sorts of things in code... hence the need to have that synergy - connecting scripted asset's complexity to Playmaker's ease of use.