once you recognize it, you may start to catch it in use in applications all over the place. if you ever use xilinx tools, ECAD, etc, you will see reams of tcl handling builds and project definitions
This is a blast from the past. All the SCO Open Server 5 sys admin tools are tcl, both the curses and gui front ends. I haven't touched it since then. I had no strong opinion about it either way at the time.
Network effects. John Ousterhout invented tcl in part to script/implement the Magic VLSI layout tool. So it's not surprising it's spread to other EDA applications.
that I couldn't tell you. I'd personally pick lua (or damn near anything else) first. maybe just entrenched knowledge/tooling in certain industries monster codebases.
Personally, I'd pick Tcl long before Lua... but I'd pick almost anything before Lua; which I find frustrating to work with. There's a _lot_ of personal preference and "feeling" that goes into what each person likes in a language.