They are forcing detainment or deportation due to lack of resources for migrants. Governors of states with sanctuary and border cities are petitioning the Federal Government for assistance to offset the cost of migrant housing. The overcrowding in some areas is very costly and difficult to manage. Border towns are also underfunded federally, requiring the state to pay for transportation to sanctuary cities.
With proper Federal legislation, there would be established funding for transportation and housing costs, taking the burden off of border states, as well as cities that offer migrant housing. We would have a way to support migrants seeking asylum nationally, rather than just the states that volunteer assistance.