I don't either. I am fascinated by the topic of how federal expenditures are justified constitutionally. Article 1 Section 8 is my friend. Perhaps we are dealing with a penumbra situation here. As Walter Williams would say, "Let's look at it."
The Congress shall have power...
OK so far.
To establish post offices and post roads;
Government at any level serves the function of being a focal point for what people need collectively, like health inspectors.
To promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries;
Patents. Copyrights. Not fine arts, and not direct funding. But certainly the intention to promote the creation of good things.
To regulate commerce with foreign nations, and among the several states, and with the Indian tribes;
Here is the big step. Anything that the states can do, which is just about anything, may need to be regulated as inter-state commerce, and this has been expanded to mean anything the states can do can also be done centrally by the federal government, as a way of consolidating efforts.
Don't shoot me. I am just the messenger.