Because we told you and you rejected it.
With greater knowledge there comes greater responsibility.
Before we told you, as Paul writes
For as many as have sinned without the law shall also perish without the law!
For when the Gentiles(gerani1248),
which had not the law,
do by nature the things contained in the law,
these,
having not the law,
are a law unto themselves:
Which shew the work of the law written in their hearts,
their conscience also bearing witness,
and their thoughts the mean
while accusing or else excusing one another!
Problem is that you have learned the Law and now know the Law.
So you are now under the Law.
You have also rejected the gift that God has offered to you to free you from your sins.
Again, with greater knowledge there comes greater responsibility.