I have a minor heart condition that i have had my entire life. my doctor cleared me for all physical activity but told me not to bench press. why?

Bench press: This will decrease the blood flow to your brain. This may cause you to pass out. All the best.

May have to ask: You may have to ask your doctor directly. Bench press is not necessarily different from other forms of resistance exercises, such as squats, military press, etc with one exception and that is there is an increased risk of blunt trauma to the chest. So, if the doctor said you can do all other exercises other than bench press it is either they are concerned about that or you might have to ask them