That way the parents are alerted of your existence and have their radar up.
That way, when you're finally ready to tell the parents that you intend to marry, you can say, "I've known this person for ___ long". And FYI..though many things are not spoken about openly... The worst thing you can do is say "I have a girlfriend" and leave it at that. Watch out for all the emotional blackmail coming your way ("You're the reason why I have high blood pressure" etc.) Once you're financially secure, tell them you "intend to marry" your foreign partner.
For this post, I also consulted dear husband-ji & my trusted traditional Telugu MIL. There is a distinct order of events within traditional Indian families - sisters must be married first, eldest to youngest; then brothers, eldest to youngest (providing they are all of a marriageable age).
A marriageable age for an Indian guy is different than an Indian girl.
In Western culture, secrets are seen as being something to be embarrassed of.