I don't understand why it can be directly used even without installing, just uncompress it and will work.
Anyone knows the reason?
I'm asking why it can be so easy?
I'm not sure what you mean. The purpose of xampp is to be easily installable. I'd not recomment it for a live system, though - it's more suitable for a developer machine, where you do not really care about making everything secure; you just want it to work.
Update, after updated question:
it can be so easy since the package comes with pre-created config files, so all you need is to uncompress and start it. No manual configuration neccesary. This is easy, but under certain circumstances it is also dangerous, that's why I do not recommend xampp and such for live systems.
When you install any other way, like from a .deb, .rpm, whatever - you get the pack, but only with the factory default config files that you will need to edit for your requirements.
They compile everything to be self-contained in the XAMPP directory. They make quite a bit of changes to how apache/php/mysql is compiled so that all binaries and libraries can find each other. They basically turn off almost all security measures to make it easier to install and configure.
If just uncompress it dont work. it must be runned after uncompression. ;-)
I remember times when all programs work in this kind.
But many programs has different requirements for os environment.
Necessary make installation to check and correct all requirements. or software must be self-sufficient and contain all required utilites and libraries.
In modern time, requirements can be huge.