I'm typing this from memory, so if anyone has corrections, I'd appreciate it.
Cobol 1968 required the use of a period to end a division name, procedure division paragraph name, or procedure division paragraph. Each data division element ended with a period.
There were no explicit scope terminators in Cobol 68, like END-IF. A period was also used to end scope. Cobol 1974 brought about some changes that didn't have anything to do with periods.
Rather than try to remember the rules for periods, Cobol programmers tended to end every sentence in a Cobol program with a period.
With the introduction of scope terminators in Cobol 1985, Cobol coders could eliminate most of the periods within a procedure division paragraph. The only periods required in the procedure division of a Cobol 85 program are the to terminate the PROCEDURE DIVISION statement, to terminate code (if any) prior to first paragraph / section header, to terminate paragraph / section header, to terminate a paragraph / section and to terminate a program (if no paragraphs / sections).
Unfortunately, this freaked out the Cobol programmers that coded to the Cobol 68 and 74 standard. To this day, many Cobol shops enforce a coding rule about ending every procedure division sentence with a period.