[dspillett]

Multi-threading was far more popular on Windows then other OSs because starting new processes was so damned expensive.

On many other systems the overhead of bringing up a new process was so much closer to that of bringing up a new thread that you only needed threads for really high performance parallel code and/or when you needed fast shared memory and/or were very memory constrained. Any time the individual tasks are fairly independent, had noticeable bottlenecks other then CPU, and data larger then the process itself, say a web server, processes were more than adequate and you don't need to worry about certain potential concurrency issues.

[nl]

Yes, this is all true. But also many threading implementations (especially Linux) back then were pretty bad. Solaris and Windows were the only places where it made sense to use them.

See also "Green Threads" in early Java implementations.