I think "tools that build tools" is a very different ecosystem from most others. When you pull in something like e.g. LLVM, you're not really having to deal wit

I think "tools that build tools" is a very different ecosystem from most others. When you pull in something like e.g. LLVM, you're not really having to deal with any of that. It's a clean bolt-in API, freely-licensed, no weird integration points, with many active users who've sanded off any weird expectations. I think the difference is that something like log4j has no pressure to be "the least power it can while doing the biggest job it can" — it has mostly enterprise customers who want the power, but don't care about the scope creep. Something like LLVM, on the other hand, has both big enterprise use-cases, and tiny embedded use-cases, with big players invested in both. So its size and scope have been much more well-considered, with any components that do something other than "compile these data structures representing inputs, into these other data structures representing outputs" having been long factored out into additional "plugin" sort of downstream-dependency libs.