There can be at least two reasons why policymakers might want to reduce poverty.
First, there is the moral factor. It seems wrong for a country like the US, with so many people who are so well-off, to have people still living in poverty. Many people see this as immoral and therefore want to fix the problem.
Second, there is a more practical factor. Poverty can destabilize a society. It can, for example, lead to more crime. Or, if it is bad enough, it can lead to a breakdown in social order. People who work hard and yet remain poor may become disenchanted with their system and inclined to rebel. This could end up seriously undermining a society and government, which is a good reason for policymakers to want to eliminate it.