If you look at all of the other moves that deal double damage against Pokemon who have used Minimize, which are Stomp, Steamroller, Body Slam, Flying Press, Heat Crash, Heavy Slam, and Malicious Moonsault, you'll realize that all of them have to do with crushing or slamming into the Pokemon that it's used on with a high amount of force. The same applies for Dragon Rush. Have you read its in game description?
The user tackles the foe while exhibiting overwhelming menace. It may also make the target flinch.
Now look at Minimize's in game description.
The user compresses all the cells in its body to raise its evasiveness.
Think of a Pokemon under the effects of Minimize as an ant as a Pokemon using one of those moves above as John Cena. I very highly doubt that an ant could survive a body slam from any human, much less John Cena.
Sources: This and this.