Earlier quoted context omitted.
Because it's dead-simple to parse? Remember that not all machines back then had hardware call-stacks.
It’s definitely easier to parse, but you can use shunting yard to do operator precedence parsing using very little extra memory and no recursion. I feel like the language is just poorly designed.
To be charitable to its original designers, information was much less easily accessible in the 1960s than today-although the shunting yard algorithm had been published in the research literature in 1961, practitioners working 5-6 years later may plausibly have been unaware of it-it wasn’t like nowadays where they could easily discover it in Wikipedia or by asking an LLM.