Actually, the rPi foundation have been extremely lazy about ARM64 support. The Pi 3 and newer support it (and I run 64bit Arch on mine), but Raspbian does not. I'd wager 95% of Pi users are stuck with 32-bit ARM software, as you have to go out of your way for ARM64 support.
If I am counting correctly, nixpkgs (NixOS) Hydra currently builds 22369 packages successfully on AArch64. IIRC also 98% of Debian unstable builds on AArch64.
So even though the rPi foundation may be slow (I don't know), the larger community has been working hard on making software build on AArch64.
To be fair, Raspbian is meant to support first-time users. They have explicitly said that they want to produce something that works for the widest range of hardware.
