Hi everyone this may be a stupid question but I recently planted a Margaret Roberts Lavender bush in a flower bed where a dead bush stood for 2 years. This past spring we removed the bush but not all of the roots were removed. That lavender bush died and I want to know if it is possible that it died because of the old roots still in the ground (nothing grows out of the roots) or was it some other factor?

EDIT

I live in South Africa. I tested the soil and it drained pretty quickly so no water pooled up at the roots. The plant got afternoon sun from 1pm until 6pm. The soil is a mix of potting soil and loam. I don't know what type of bush was previously planted there because the bush never got leaves or anything so we assumed it was dead. The roots were spongy.