Perhaps it may be a combination of close neighborliness, a small means of transportation of antiquity such as a bicycle cart, and a sense that is more fitting to the human scale.
Settlements in antiquity were governed by different principles of spatial planning and communication and transport system than today. Given the fact that the technological level was low, there was no development of transport. In this sense, settlements were small, with people moving around on foot or with animals because of the relatively short distances. The lack of means of transport does not imply the formation of a street network that takes this into account. Rather, it is oriented towards individual travel on foot. Therefore, streets were built more easily and in accordance with the conditions and way of life in antiquity. These conditions set the way the urban area was organized and laid out, which explains why large houses were made into the narrow walking way streets.
Ancient cities were designed for pedestrians since the mode of transportation back then was predominantly by foot, or on an animal. The scale of the buildings, the street width, the relationship between the building and the street etc are therefore, of human scale Also, narrow roads help create better micro-climatic conditions, especially in hot regions, where narrow streets remain shaded by the abutting buildings throughout the day.
The way of life of people in ancient times and the way of transport are very different from nowadays. First of all, design is always for the purpose of use, ancient people basically walk, at most two-wheeled vehicles or tricycles for walking or as a tool vehicle, and do not need to use too wide roads. Secondly, the ancient design perspective is not as multidimensional as the modern design perspective. That's why ancient houses were built on both sides of narrow roads.