The initial release of dnsmasq was in 2001. The list of viable languages for a high-performance network server at the time was still not all that long. Erlang wasn't on it. Too big a performance hit, too much opaque runtime that may not have been stable at the time, too few contributors, big dependency footprint of stuff most things wouldn't have installed. (When I used Erlang for a production system in more like the 2015 time frame it still had rough corners if you weren't using it exactly for the use case it was meant for.) This isn't specially a criticism of Erlang, it would have been like this across many languages and runtimes.
A lot of these systems that are getting hit, and will probably continue to be hit over the next few weeks or months, have a similar story. The Linux kernel's only other potentially viable choice was C++ at the time. OpenSSL, a perennial security offender, was started in 1998. You can look up your own favorite major system library with major security issues and it's probably the same story.
I'm as aggressive as anyone about saying "don't write a new project in C for network access", but cast me back to 1998 and I couldn't tell you what other viable choices there are either. There are safer languages, but they were much, much smaller than the C community, and I couldn't promise you how stable they were either. Java was out, and I don't know when to draw the exact line as to when it became a serious contender for a network server, but late 200Xs would be my guess; certainly what I saw in 1999 wasn't yet.
Example: I ran a Haskell network server in 2011 for something relatively unimportant and it fell over under conditions that would not have been very extreme for a production network; I know it was Haskell and not my code because I reused the same code base in 2013 with no changes in the core run loop and it did about 90% better; still not enough that I would have put that system into a real production use case but enough to show it wasn't my code failing. So while Haskell may have existed in the 200Xs, it wouldn't have qualified as a viable choice for a network server at the time.
There's a lot more viable choices today than there used to be.