The army deployed in Texas cost more each year than the total number of $ Collected in the south as Tariffs.The North would not just leave the South alone because it was simply too important to be allowed to withdraw from the Union. The North would have lost valuable territory and resources if the South had seceded. First of all, the South contained valuable government property that would have been lost such as forts, arsenals, U.S. mints, custom houses, ship yards and other assets. In addition, the North would have lost the tax revenues generated in the South through the collection of the federal tariff which was an important source of funding for the federal government..
Then add the expenses for other facilities in the south.
For the federal government, "owning the south" was bad for the federal economy,