It depends a lot on when.

For pure research V7 / 2BSD / 4BSD that was true. You can give the install.ms from these releases as a reference. It was a lot more daunting than today, and often times only bug fixes warranted a recompile. You can find references in the 2.11BSD patch series to the 'annual recompilation of the sources' which Steve did and where he'd always find something.

However, after that, everything was binaries. The kernel you got was a bunch of .o files (even for the V7 ports), though often you had all the source to the drivers (but not the core of the kernel). I have said files for Venix, though there it was an extra cost option it seems (I say seems, since I've not found a price sheet for it from the era, though I have the disks). DEC's ultrix was binary. Sun's SunOS. All the Unisoft ports to 68k machines. Sony's NEWS workstations likewise. HP's unix offerings too. Sure, you could get a source license, sometimes, but they kept those expensive.

IBM and VMS were always binary only (though again, you could buy source if you had the right amount of $$$ and leverage).

So I'm not sure what old days you were talking about, or which machines....  The BSD build.sh and/or make world were a bit of an anomaly imho. Once Linux got distributions the whole notion of building it yourself faded somewhat.

Warner