Also because the special characters were (and are) difficult to type on European keyboards.
Characters like []{}\|~ are behind multi-finger access and often not printed at all on the physical keys (at least in the past). You can see how this adds a hurdle to writing C…
Pascal was designed by a European, so he preferred keywords which could be typed on every international keyboard. C basically just used every symbol from 7-bit ASCII that happened to be on the keyboards in Bell Labs.
Just as example, on my slovenian QWERTZ layout: [ - altgr+f, ] - altgr+g, { - altgr+b, } - altgr+n, \ - altgr+q, | - altgr+w, ~ - altgr+1.
You get used to them, though you start feeling like a pianist after a short coding session. The one most annoying for me are the fancy javascript/typescript quotes, which I have to use all too often: ` - altgr+7.
I tried switching to US a few times, but every time muscle memory made me give up soonish - especially since there are big benefits to using same keyboard layout as other people in your office are using.
Also practically everytime I need to write a comment, commit message or email I need my č, š and ž. It's kinda nice to have them only a single keypress away.
I'm from a non-English country. I only ever use layout of my locale when I write in my language. That's how it was ever since I was a kid who knew little English. And that's how all computers I've encountered in my country are set up - English first, local second.
In addition, our layout, overwrites only the numerics – all other symbols are the same as on a US layout.
Spectacular?? Terrifying. If I need to type non-ASCII Latin characters I'll just use compose sequences. The thought of a non-U.S. keyboard layout with modifiers required to type []{}<> and so on is terrifying.
I think in Europe C was not as common as other languages at the time so the terseness looked odd.