gzipping documents is a long tradition. Most common text reading tools (cat, more, less, grep, diff, and some more) has "z" variants which work on gzipped files directly, without ungzipping them.
Most of the tools bigger documentations come in man and info files. If there's an even bigger, additional documentation, it comes with -doc package (like apache2-doc).
Otherwise every package comes with some basic documentation and Debian specific changes file, most of the time.
Debian's specifics on packaging is very strict. You just cannot package something and publish in the main repo.
It was always somewhat annoying though, particularly when it broke inter-document links, and it was a legacy of older times. Today, it's way past time to drop individual file compression. I mean, we have transparent compression with systems like ZFS, so there's no penalty to pay by half-assing it with gzip.
If Linux was a big-iron only OS, I could happily agree but, this stubborn thing works from Raspberries to mainframes and everything in between. So it's not always possible to run it on a CPU which can drive an ZFS on a multi-disk enclosure.
I'd rather have individually compressed files instead of running a heavier FS layer with smaller/less powerful systems.
Most of the tools bigger documentations come in man and info files. If there's an even bigger, additional documentation, it comes with -doc package (like apache2-doc).
Otherwise every package comes with some basic documentation and Debian specific changes file, most of the time.
Debian's specifics on packaging is very strict. You just cannot package something and publish in the main repo.