Maybe not your infant, but this is certainly not any sort of universal truth. Possibly you could argue that physically attending to the infant themselves is not a full time job, but all of the associated tasks in maintaining any sort of functional environment (food, dishes, laundry, etc. etc.) is, at least to me, at least a 9-5 job.
Our son demanded by wailing or screaming to be held during all waking until at least 12 months, including sleeping for more than 10 minutes alone. I worked from home during this period and I cannot fathom having been at home alone with him and attending any meeting or focusing on a task in a realistically productive way.