Wirth was obsessed with the idea of creating the absolutely minimal useful language, and many of his languages' warts come from that.

Variables are at the top because:

- you immediately see them (so, perhaps, easier to reason about a function? I dunno)

- the compiler is significantly simplified (all of Wirths' languages compile superfast and, if I'm not mistaken, all are single-pass compilers)

However, I feel that Wirth was overly dogmatic on his approaches. And "variables must always be at the top" is one of those.