If you didn't know that this wasn't always the case, you are definitely not the only one. Emergency rooms throughout the country still have people coming in with late stage disease, amazed at their status, saying;
"I had a blood test 3 years ago when I had the flu...the doctors would have told me if I had HIV."
No, they wouldn't have because they were not allowed to test without your explicit consent. Also, if you get a test, the clinician needs to provide you with several minutes of pre-test counseling including safer sex practices.
Now (finally) the CDC has decided that it is worth the lives it will save (though why we start at 13 and end at 64 is beyond me) to add the test to your round of cholesterol, blood chemistries and other tests unless you specifically decide to opt out.
It is estimated that about 25% of the people in this country with HIV infection don't know it. It also, so happens that if you don't know you have HIV, you are far more likely to transmit it to someone else.
Making testing a part of routine clinical care is a long time coming and will make it more likely that people who have HIV will get appropriate medical care earlier than they would have if they had waited to find a clinic that did testing or a doctor finally got around to asking them if they wanted a test.