A lot of the foundational layers of software are quite old. Kernel: Linux/Darwin, Compiler: GCC/LLVM, Database: Postgres/MySQL/SQLite, Browser: V8/WebKit.
The more low-level, the older it gets.
The industry is still extremely young. It's hard to imagine that we won't eventually rewrite everything in time.
What do you think will be re-written, and what benefits will it bring?