Why shadowJar minimise() is not removing all unused dependencies?

Question

I'm trying to generate two different jars from a project which is a monorepo that includes dependencies to many many great things in this world, so needless to say i do not want these executable jars to have big sizes and would rather have them include only classes that they actually use.

I followed instructions here https://imperceptiblethoughts.com/shadow/configuration/minimizing/.

In order to test if shadowJar task actually works i created a simple Main java file that practically uses nothing other than java SDK.

public class Main {
    public static void main(String[] args) {
        System.out.println("client");
    }
}

and added the actual shadow jar task and pointed to this as a main class

shadowJar {
    archiveBaseName.set('client')
    archiveClassifier.set('')
    archiveVersion.set('0.1')
    minimize()

    manifest {
        attributes 'Main-Class': 'my.package.Main'
    }
}

which generates the uber jar correctly (i was able to run it simply with java -jar ...), however the size of the file is 10Mb.

then i generated a new version without minimize() part and it was 15Mb.

Is there something i do wrong here? Maybe i'm expecting too much from this tool and proguard (as tedious as it is to setup) is the only way?