For one, many investigators are seemingly unaware of how their research animals are housed. If scientists don't care enough to verify that the research animals they use are housed in accordance with sound scientific methodological principles, there is little hope that they will support efforts to refine current housing practices. Another consideration is money some would say greed. It is certainly true that upgrading cheap monkey housing conditions requires additional financial investment, but this initial investment will quickly yield important returns. Better housing conditions will lead to more valid scientific data, therefore reducing the number of animals needed to obtain the information.
Money is saved and animals' lives are spared.