It's been a while since I looked into it, but I opted to stick with MacPorts rather than Homebrew in large part because I got the impression that Homebrew wanted to own /usr/local rather than sharing it with other software. (Maybe that's inaccurate?) I still occasionally compile software by hand rather than through a package manager, and /usr/local has been the default target for a system-wide install on every Unix-style system that I've used in the past 20-ish years.

(Also, my wife and I both have active accounts on my machine, which makes me uneasy having files in a systemwide directory like /usr/local owned by one specific user. That also feels distinctly non-standard to me.)