Big power poles are chosen because:
1) It forces you to do bigtime metallurgy by foundry to craft enough. Even though you can technically do this on other planets, Vulcanus is uniquely well suited to actually pumping out that much metal. This solves the core issue that Vulcanus is the metallurgy planet, but you don’t actually need to take advantage of that in base spage.
2) Thematically, it is a giant metal structure of basic metal (with no circuitry in the recipe).
3) Big pole lets you compactly consolidate a lot of metal through a very fast recipe that allows for an upgrade with another planet’s upgrade (EMP from fulgora) later on. Recipes like assemblers or chem plants aren’t good for this. Consolidating these intermediates is much better to build with than a science recipe that directly requires 5 different items as input to achieve the same result.
4) Big pole specifically takes advantage of the variety of cast recipes to directly get several intermediates (steel, cable, sticks) which normally take more steps without the Foundry.
5) It’s actually used on Vulcanus.
Nothing else really matches these criteria, as excluding circuits severely restricts the pool of decent candidates. There are some other recipe choices like heat pipes, steam turbines, heat exchangers, or armor. However these all have worse gameplay for taking advantage of the foundry’s repetoire of casting recipes AND worse theming (most of these aren’t even needed on Vulcanus!). The next closest thing is the medium power pole, which is the same thing, but subjectively slightly worse for theming.
