That's just the way it was coded. From SAS's documentation:
This statement suppresses a title on linenand all lines after it: (Where n is a number between 1 and 10)
titlen;
A TITLE statement for a given line cancels the previous TITLE statement for that line and for all lines with larger n numbers. TITLE with no number assumes TITLE1.
That's the design, and it's a good one. Wouldn't it be annoying if you had to cancel all of the titles by specifying separate statements each time you wanted to change them? Yes, it could have been designed other ways, but that is how it has worked when I first learned SAS '79.