We used to have milkweed here but most of it has been tractored down or land development and urban sprawl has destroyed it --as well as many other native plants. You are lucky that your city areas still have milkweed. It will be a matter of time that the milkweed in your location is gone as well.
illegal logging in Mexico destroying the Monarch butterflies' Winter roosting areas, and destruction of too many Eucalyptus trees in California (another monarch Winter roosting area) reallly does put the monarch on the endangered list.
These problems for the monarch butterfly have only started later in this decade. I don't think that they stand too much of a chance.
Yes, GMO crops and herbicides/pesticides are a major culprit as well- and I continue to petition against that-- however, that is not going to discourage me from planting organic milkweed to make up for what was destroyed in my area-- OR buy monarch butterfly larvea to hatch and set free in my rural neighborhood.