"We were speaking loudly while they were telling stories."

"Noi vorbeam tare în timp ce ei spuneau povești" should be also accepted (they were telling stories = ei spuneau povești)

Is there a reason why this was marked as wrong when I wrote "Vorbeam tare în timp ce spuneau povești", singling out that I had omitted "ei"? In many instances it appears that pronouns aren't required - is the "ei" necessary here?