The Maasai, much like many other sub-saharan communities have long lived a semi-nomadic pastoral lifestyle; basing survival on livestock: as both food and currency. For several thousand years, this had been done sustainably in the grassy savannahs where cattle were able to graze freely. In the past century, however, there has been a large push to conserve certain areas of land in attempts to preserve the species that thrive in those environments.
The general consensus of this movement was that human interaction with the land and animals was leading to species endangerment in addition to land pollution. Granted, this is very true of many of the humans not indigenous to the lands. The people who had been living on this land for centuries beforehand, however, were abruptly forced to move. In some cases, like the Maasai, this happened multiple times over the course of the 20th century. Not only is this jarring to the cultural psyche, but is also damaging to the sustainability of the pastoral lifestyle that the Maasai hold on to so dearly. In the past, the herds of Maasai cattle had free access to a surplus of grazing land, which in turn, was able to sustain the Maasai people indefinitely. Having now been pushed off said lush land, the Maasai have been forced to forsake their traditional nomadic pastoral lifestyles for pseudo-sedentary agro-pastoral ones. Granted, this may not seem immediately problematic, however, there are many factors that lead to this lifestyle being less easily sustainable, especially in the hot, arid environment the Maasai find themselves forced into now.
As fervent pastoralists by culture, the Maasai simply do not have much interest in agriculture, perceiving it as being solely meant for the livestock.
With 595mm of rainfall annually, most regularly harvestable crops would have trouble growing.
Through sedentary life, populations have a tendency to rise, and without adequate ability to sustain that growth, there will be widespread malnutrition
Sources:
McCabe, J., Perkin, S., & Schofield, C. (1992). Can Conservation and Development be Coupled among Pastoral People? An Examination of the Maasai of the Ngorongoro Conservation Area, Tanzania. Human Organization, 51(4), 353–366. https://doi.org/10.17730/humo.51.4.d20010q600v50240
Muhumuza, R. (2018, May 12). Thousands of Tanzania’s Maasai evicted from their land “for tourism.” Retrieved September 26, 2018, from https://www.smh.com.au/world/africa/thousands-of-tanzania-s-maasai-evicted-from-their-land-for-tourism-20180511-p4zert.html