Why are software installations so difficult

After paying a large price for software, one feels that it is all done with and one can start using it. But unfortunately it is easier said than done, if a person has not installed it earlier he either has to pay a charge for the installation to the vendor or go through an installation manual of over 500 pages and attempt to install it. After following the instructions in the manual, snags arise. To solve the snag, the product support site needs to be accessed and what is found that a patch needs to be downloaded to proceed ahead! The least a vendor should do is to provide self installing software without the administrator going through pages and pages of manuals and downloading fixes and rather unfortunately when the next version comes out the installation procedure changes. Sigh!