In the beginning Sun released
Java 1.0.
Then they stood back and looked at what they had made, and saw that all was not good.
And on the second release (1.1) they made it better.
And on the next release (1.1.x) it was better still.
And on the 1.2 release Sun created collections etc. and many of the early classes became obsolete.
However there remained much code that still used the old ways. In it's wisdom Sun did not want to break that code, and therefore left the
legacy classes in place and these were marked "deprecated". In addition many methods of "improved" classes were marked "deprecated" to show the people the new way.
And Sun said "thou shalt start replacing this stuff, cuz we aren't going to wait forever to get rid of it".
And the people (did what???).