At the time, Todd was testing with whatever the popular rop compiler was, and it wasn't able to chain anything using libc. Even on amd64 you can restrict which gadgets are available. Maybe you can find other approaches with a careful hand search, but I think knocking out the biggest exploit generator is hardly flawed in a practical sense.
CTF challenges are to cooking competitions what exploit development is to being a restaurant cook. There are time limits, practicality is less of a concern, and everyone knows that toy constraints are added because nobody wants to watch you stare at IDA for three weeks
