It is kind of amazing where the build process is[0][1].
0. https://buildd.debian.org/status/architecture.php?a=riscv64&...
0. https://buildd.debian.org/status/architecture.php?a=riscv64&...
E.g. arm64 dropped very low for a while or all arches dropped around 2024.68
If there's a huge drop, it is most of the time because a package a lot of software depends on got updated or modified (e.g. built with different options) and it caused ABI changes, thus causing rebuilds of everything that depends on it.