The full TexLive distribution contains all officially accepted packages ever written (this includes fonts, iconography, compiled documentation and other heavy stuff), most of the compilers, the LaTeX and Context (MK II and IV) packages and a huge toolchain. For compatibility reasons, packages are (almost) never removed. Also for compatibility reasons, the LPPL (Latex Project Public License) discourages[1] the release of a modified package under the same name, so there are copies within the distribution.

So, the TexLive distribution is the "fire-and-forget"-package in the LaTeX world, thats why it is so big. I use it for around 10 years now and I never had to install an additional package.

[1] It even prohibited that for a while, see Wikipedia.