This is fascinating!
I started with BBC Basic II (on the Model B) which had IF..THEN but it was just one line and there was no ELSE. So if you wanted to make a 'block' you had to call a different PROC (thankfully there were PROCedures so you could avoid GOTO)
As such when I was introduced to ELSE and ENDIF with BBC BASIC V on the Archimedes it seemed like very welcome syntactic sugar - it let you do the same stuff but in a tidier way