古代西藏是一个位于高原地区的边远地区，其特殊的地理环境和气候条件对当地人民的生活方式产生了深远的影响。在这个地区，人们往往倾向于以畜牧业为主要的经济活动，而蔬菜则相对较少被当作食物消费。这主要是由于以下几个原因：

首先，高原地区的土壤和气候条件不利于蔬菜的种植。古代西藏大部分地区都位于海拔3000米以上的高原地带，这里的土壤贫瘠，水源匮乏，以及气温变化幅度大，日照时间短。这样的自然条件对许多蔬菜的生长都造成了不利影响，使得蔬菜的种植面临很大的困难。

In ancient Tibet, people tended to eat less vegetables mainly due to the unique geographical environment and climate conditions of the remote highland region. In this area, people often relied on animal husbandry as the main economic activity, while vegetables were relatively less consumed as food. This is mainly attributed to several reasons.

Firstly, the soil and climate conditions in highland areas are not favorable for vegetable cultivation. Most parts of ancient Tibet were located at an altitude of over 3,000 meters, where the soil is infertile and water resources are scarce. Additionally, the temperature variations are wide and the sunlight exposure is limited. These natural conditions pose great challenges for the growth of many vegetables, making vegetable cultivation difficult.

其次，交通运输条件的限制也导致蔬菜的供应不足。古代西藏地处高山峻岭之中，与外界交通非常困难。在没有现代化交通工具的时代，无法快速、有效地将大量的蔬菜从远地运输到西藏，这也限制了当地人民对蔬菜的获取数量。

Furthermore, the limitations in transportation also resulted in inadequate vegetable supply. Ancient Tibet was situated amidst high mountains and rugged terrains, making it difficult to access from the outside world. In the absence of modern transportation, it was not feasible to transport a large quantity of vegetables from distant places to Tibet in a quick and efficient manner. This restricted the local people's access to an abundant supply of vegetables.

此外，古代西藏的文化和饮食习惯也对蔬菜的消费产生了影响。在西藏的传统饮食中，以肉类和牛奶制品为主要食物，而蔬菜在整个饮食结构中所占比例较小。这一部分是因为长期以来的农牧业经济导致当地人民的饮食结构倾向于畜牧食品，同时也与地理环境中缺少大规模蔬菜种植有关。

Moreover, the cultural and dietary habits in ancient Tibet also influenced the consumption of vegetables. Traditional Tibetan cuisine mainly consists of meat and dairy products, with vegetables playing a lesser role in the overall food structure. This can be attributed partly to the predominance of animal husbandry in the local economy over a long period of time, as well as the lack of large-scale vegetable cultivation due to the geographical environment.

总结起来，古代西藏之所以少吃蔬菜，主要是由于高原地区的土壤和气候条件不利于蔬菜的生长，交通运输限制了蔬菜的供应，并且当地的文化和饮食习惯也与蔬菜消费的相对较少有关。然而，随着科学技术的进步和交通运输的改善，如今的西藏已经能够更加便捷地获取蔬菜供应，人们的饮食结构也逐渐发生了变化。

In conclusion, the limited consumption of vegetables in ancient Tibet was mainly due to the unfavorable soil and climate conditions for vegetable cultivation in highland areas, transportation constraints on vegetable supply, and the cultural and dietary habits that emphasized more on animal-based food. However, with the advancement of science and technology and the improvement in transportation, nowadays Tibet has been able to access vegetable supply more conveniently, leading to gradual changes in people's dietary structure.