How come the logons and bootskins are in a format that BootSkin and Logon Studio cannot read?

I am slightly confused as to why, for example, logons and bootskins are downloaded as .zip files with various files in them, when the programs that this site recommends to use to install them requires a different format? I discovered that copying the zipped folder contents into the programs directory allows access, but why is is so complicated?
For example, with DogmaX bootskin, I use bootskin to load, but it asks for a .bootskin file. However, the zip contains a .bmp and a bootskin.ini file, which Bootskin did not recognize. The same goes for LogonSudio, which wants a .LogonXP file, but the dogmaX download has a whole bunch of files wiht a theme.ini and a uifile.txt file instead.