It is real simple: thru Adam all mankind became sick, thru Jesus Christ all mankind is and will be made well.
Otherwise, you believe the power of sin, Adams failure (the sickness) is more powerful than Jesus' obedience (the medicine).
Romans 5
:15 But the gracious gift is not like the transgression.19 For if the
many died through the transgression of the one man,20 how much more did the grace of God and the gift by the grace of the one man Jesus Christ multiply to the
many!
The VERY same "many" in both cases!!