“The point is that these funds allow many states to construct transportation infrastructure that they wouldn’t be able to afford without it.”
That is patently false. If the monies were kept in their states (lowering federal taxes), state taxes could capture it and fund the projects. Instead we get the corruption of Congress that turns federal funding into pork barrel projects and as far as fuel taxes go many of the projects it funds often have zero zip nada to do with transportation.
Or they wouldn't build the projects at all -- even if they were projects of national significance.
Perfect case in point: the Alameda Corridor initiative in southern California, along a busy rail corridor that connects the Ports of Los Angeles and Long Beach to the interior of California. Something like 80% of the cargo moving through these two major ports is destined for points in the U.S. that are hundreds and thousands of miles away. The upgrades along this route involved both public and private partners (eliminating grade crossings where public streets crossed the railroads), and were aimed at improving the throughput of the rail system between California and the rest of the U.S.
If it were up to California alone to fund this whole thing, it would never get done. California would simply have plenty of better things to do with their fuel tax revenues than to improve the flow of freight through LA/Long Beach to Midwestern rail hubs like Chicago and Kansas City.
You see variations of this story repeated all over the country ... which is why major transportation projects often meet overlapping local, regional and national needs.