The reason is one build tool which now requires SSE4.1 instruction support to run.
Rant
This instruction is ancient. According to multiple people on HackerNews they’re still using Opteron servers! No wonder the builds take so long, a cheap NUC would be faster.
i’m surprised they’re using prebuilt binary toolchains
There have been efforts to create free rebuilds of the SDK: https://forum.f-droid.org/t/open-source-android-development-tools/30599/136