It's the tone. yao sounds very different from liu because of the tone. yi also sounds different from liu because of the tone. yi does not sound very different from qi, and yi is hard to disambiguate with multiple yi in a row.

you use yao because it's easier to understand

qi yao yao yao ba san

than

qi yi yi yi ba san

It's mostly the qi yi yi / yi yi yi that gets hard to disambiguate.

What is likely happening is that you don't yet have the ear for the tone.