I'm perplexed at this statement, and the rest of your post in general. How is that "inefficient"? What else can the thread do if it needs to process data that hasn't arrived yet?

Some other task, such as processing data from a different socket that has arrived now. A library monopolising a thread for this one operation is like those DOS-era applications that expected to monopolise the whole CPU for their application - sure, it's "simpler", but it's vastly less efficient.

(And doing your network I/O async should not be complex or confusing in any serious modern language)