That's not really a problem with serving web requests. Usually there isn't a downside to multiprocessing these. I don't know anything about this framework but I assume it is using some sort of non-blocking IO which works just about as well as OS threads for web servers. Look at something like Gevent if you are interested in this.
The problem is that sometimes you do need to do some heavy processing while servicing a request, and then you're blocking all other users.
Event-driven processing is much like cooperative multitasking from the Windows 3.1 days. It only works well if every part of the machinery behaves properly and predictively.
