Comment by MarkusQ

That's more of a compiler limitation that became cultural for a while. Most languages (both natural and artificial) use delimited structures sparingly and rely more on other cues. It sometimes appears spontaneously (e.g. "∫ dx f(x)" is logically fine, but feels wrong) but in general it's rare.

The move away from indentation in programing came as a rebellion against the too-constraining fixed column languages, in the interval between punched cards and python, with a brief resurgence in the early blink tag and font potpourri web era. These days, it's perfectly reasonable.