Closing roads completely to deliver construction projects more quickly makes sense.
The time to be spent on the work, and therefore the scale of disruption to passengers getting to and from the station, is limited, as well as the benefits of being able to conduct all work free of safety considerations needed when public are still using the services.
There are benefits to maintaining access throughout construction, especially when work is on a large scale, but in this case of Eastbourne Terrace and Paddington, the short and sharp approach is best.
Image c. Tommy Ironic