Just tried this minus (or dash) sign after a package and yes , apt-get acting like remove.

Funny thing is I didn't know this function of apt-get . This minus sign is valid for every package . I tried with smplayer- with firefox- and always acting like remove.
So the only thing I can think is that the dash sign at the end of a package considered by apt-get like a minus and install command converted to remove.

If you wanted to install everything about python3 , then you had to add an asterisk sign after this dash(minus) sign

sudo apt-get install python3-*

In the begin I thought this was just a conflict issue , but is not. Sometimes when you install some package and conflict with an other package then the already installed package will be removed due to new installed package , but this is not our situation here.

We've learned something useful today.

From the man-page of apt-get . To read the man-page via your terminal give man apt-get

If a hyphen (-) is appended to the package name (with no intervening
space), the identified package will be removed if it is currently
installed. Similarly a plus sign (+) can be used to designate a
package to install. These latter features may be used to override
decisions made by apt-get's conflict resolution system.

Eventually is not a new option or something weird , is just we don't read the man-pages carefully.