A free trial version of a software is just a trial version... Should be used to test functionality, not create completed stuff.
A critical part of that functionality is the ease with which the software handles publishing games. Personally, before committing to a subscription I'd like to be confident that the software can handle the development process from start to finish.
Ultimately, the purpose of the free version is to encourage users to take out a subscription; perhaps it doesn't lead to a greater conversion rate after all, or the technical and logistical hurdles of restricting exports to just the arcade render it non-viable, but if being able to share a game easily increases that likelihood and it's not unfeasible to implement then it would be a feature to consider.
But like I said, Tom and Ashley have their reasons for the current model and I'm cool with that :-)