A lot of the reason depends upon what you hope to get from the labour and the overall environment that you are working within.
I was working with a 486 around 1995. Compiling your own software was the norm and compiling your own kernel could have significant performance benefits (even if it was just to conserve the limited memory supported by machines of the day, to head off some of the swapping). By the time I learned of Gentoo, that was not really the case: most of the software one could obtain was provided in binary form and compiler optimizations were much less relevant (unless you had a special workload).
The tooling provided is important too. I was using NetBSD for a while. For the most part you just started the compilation process and walked away until it was done. (I imagine Portage is similar.) You didn't get the instant gratification, but it was not time intensive in the sense that you had to attend to the process. That was very much unlike my earlier experiences in compiling software for Linux, stuff that isn't in the repos, since it did have to be attended to.
It surely wasn't the norm for me, in 1995's Summer, I got my first Linux distribution via Slackware 2.0, everything was already compiled and when chosing to download tarballs I would rather pick already compiled ones.
Later on, to take advantage of my Pentium based computer, I would get Mandrake, with its i585 optimized packages.
Most of my Linux based software would be sourced via Linux magazines CD-ROMs, or Walnut Creek CD-ROM collections.
I was working with a 486 around 1995. Compiling your own software was the norm and compiling your own kernel could have significant performance benefits (even if it was just to conserve the limited memory supported by machines of the day, to head off some of the swapping). By the time I learned of Gentoo, that was not really the case: most of the software one could obtain was provided in binary form and compiler optimizations were much less relevant (unless you had a special workload).
The tooling provided is important too. I was using NetBSD for a while. For the most part you just started the compilation process and walked away until it was done. (I imagine Portage is similar.) You didn't get the instant gratification, but it was not time intensive in the sense that you had to attend to the process. That was very much unlike my earlier experiences in compiling software for Linux, stuff that isn't in the repos, since it did have to be attended to.