Why do modern tanks have smoothbore main guns?

The Challenger 2 has a rifled 120mm gun. The Challenger 3, announced in 2021, has a smoothbore 120mm. Why? Why did Britain take so long to make the big switch? What are the real advantages of each type of armament? DISCORD: https://discord.gg/WJzJXkjH3Q All simulations from: https://youtube.com/@SYsimulations https://youtube.com/@dejmianxyzsimulations4174 All content is presented in historical context for educational purposes. All footage is owned by it's copyright holder and is used in this channel under "fair use". Music by Epidemic Sound