^ Wow, the list of packages is huge...
There seems a slight misunderstanding
All of those packages are not installed on your system! Some of them are, but not all of them.
"apt-cache rdepends multiarch-support" will also list those packages that are not installed but pre-requires "multiarch-support".
Much more better way of finding the installed-only list is following,
apt-rdepends --state-follow=Installed --state-show=Installed multiarch-support
You will need "apt-rdepends" package installed for the above command.
Yet another way of doing the same is with "aptitude",
aptitude why multiarch-support
Output is not as detailed as "apt-rdepends" but should be good-enough for most cases.