That's just how James Gosling described Java when he explained the philosophy behind it in 1997[1]. He wrote, "Java is a blue collar language. It’s not PhD thesis material but a language for a job. Java feels very familiar to many different programmers because I had a very strong tendency to prefer things that had been used a lot over things that just sounded like a good idea." He most certainly didn't intend the term to be demeaning, but more to contrast it with research languages that include features that are untried and unproven. The term has since been used as shorthand for Java's (and languages like it) goals and philosophy.

[1]: http://dfjug.org/thefeelofjava.pdf