Because keeping secrets generally results in more positive outcomes than disclosing them.

Keeping a secret/lying about subjects that are important to another party is a gamble that you won't be exposed.

If the secret/lie comes out later, then the consequences are often far worse than they would have been if you had been honest.

If you have lied or deliberately misled, everything you have ever said might be up for questioning.

Now I know, and knowing is half the battle!

Or rather, ...generally are initially expected to result...