"Is the Gospel simple?"

"Shouldn't it be? Isn't that the point?"

"If it is simple, then why do so many people get it wrong?"

The Gospel is not primarily about the Salvation of man. Salvation is only the means (where both means and end are important). We are saved so we may have a right relationship with God, and glorify God through Christ, for that was mankind's original purpose before the fall. The Gospel is about restoring our very purpose of existence, to glorify God and enjoy Him forever. The Gospel ultimately isn't about us, it is about Christ and always has been.

I guess it is simple, but we've looked at it the wrong way for so long.

For this reason also, God highly exalted Him, and bestowed on Him the name which is above every name, so that at the name of Jesus every knee will bow, of those who are in heaven and on earth and under the earth, and that every tongue will confess that Jesus Christ is Lord, to the glory of God the Father.
Philippians 2:9-11 NASB

Analogy: Think of it this way. Imagine one day you get water on your computer, or accidentally dropped your phone into the lake, or your car breaks down. Your phone, your computer, your car can no longer function as intended. Jesus comes and fixes your item. He is the electrician, the technician, the mechanic, the carpenter, the healer, the savior. He gives you back your phone, your computer, your car. But if all you do is proclaim "ah! It is now fixed!" but never go and start using your phone or computer, or drive around your car, then whats the point? Is there that much difference from before when it was broken? The Gospel tells us that it is our very soul and spirit that was broken, and Jesus healed our spirit. But was there a purpose for that spirit before it was broken by sin? The Gospel should say (and does) something about that too.