Why are all my played games on lichess accessible to everyone who knows my username??

Dear Lichess-Team,
I love this site and I think it's one of the best! Great work! Thank you!
I have only one problem:
Anyone who knows my username on Lichess can easily preparate against me in a "real" match outside lichess because he has access to all my games on your site, even if he is not my lichess-friend!
For that reason I have to be very careful not telling my username to anybody.
Why has it to be this way?
Wouldn't it be better if every lichess-user could decide for his own whether and whom to allow access to his personal game-database or not?
Thank you in advance for your attention.
Kind regards from Berlin.

This has happened to me when someone from my club looked up my online games. The 1st team and 2nd team both made it to the final of a club tournament. My opponent looked up my games and had something prepared, but i had considered this so i prepared something unusual for that game. If it is this sort of thing you are worried about, then you aren't considering the potential to turn this to your advantage.. ;)

I don't see any advantage, if everyone has access to your whole repertoire! Once your username is known, you never know who is next to use it against you!
I don't see a good reason why every single game I play on lichess has to be published. Every user should have the posibility to deny accsess to their personal games!

@Mattador what's your fide rating? I mean if it is above 2000 then everyone knows your repertoire, its not a secret anymore:)

Mattador has a point.

High ranked players usually have got a wide repertory, because they have spent a lot of time studying chess. But for average players is quite tricky, because the rely on a pair of openings for white an black; and they don't have time to prepare novelties every time.
If they study a new opening, they must use it many times, to get pay back for the time investment.

I guess if many people creates double or triple nicks for this reason.

My current rating is 2025, but i haven't been playing for a long time. There are not many of my games in the chessbase database. Apart from that I have changed my whole repertoire and I just would like to avoid that some of my opponents may have access to tousands(!) of my recently played games!!