100% of all railroad steel is recycled... Eventually
On the active railroads (which you should not be walking on, by the way), you're seeing evidence of recent maintenance-of-way.
It is SOP in the rail business to pre-position supplies weeks or months in advance, and then take up to a year to pick up the old scrap. That is because of MoW priorities - they need to do work on northern climes while the weather is favorable, so work in Texas may get put on hold for months... Or traffic conditions, railroad is too busy to hand it to MoW forces for an afternoon... Or simple availability of the machines - it would be insane to pay crews to pick it up by hand when they have a Giant Magnet Machine that can pick it all up while traversing at 10 miles per hour (which matters due to track downtime). But they may have only two Machines in 20,000 miles of track, so they have to wait, wait, wait for the beast's availability.
It's typical for your basic suburban NIMBY type to figure that trains are yesterday's news, and all those tracks oughta just dry up and die. However that is not true at all. Rail moves 40% of America's ton-miles, and is the only way your local Target or Ikea store keeps its shelves stocked. Rail can move 1 ton of freight 460 miles on 1 gallon of fuel, so this is actually fairly "eco" conpared to trucks - nevermind that two train crew can move 20,000 tons of freight as opposed to only 80 tons if they were truck drivers.
Further, rail is the only transport mode that lends itself to electrification, so it could clean up as the grid does. It's also our best hope for mass intercity transport that is 100% renewable, and remember, French TGV rails are essentially identical to better freight rails. Heck, the John Bull could celebrate its 150th anniversary by steaming down any random freight line, the Acela line, or indeed, the TGV lines. They are that compatible. And nobody ever complained about railroad electrification using minerals that are toxic to manufacture - it's just steel, copper and aluminum.
Removal of a rail line is an environmental nightmare
That dormant (not abandoned) rails-in-place rail line can always be reactivated. Which means industry can go right back to taking rail service, or passenger lines can be extended on the cheap. It costs between $5,000 and $250,000 a mile to reactivate a dormant line. Even if the line needs 100% replacement of ties, rails and ballast (pushing $1 million a mile), the old rails allow use of on-rail mechanized repair equipment and direct delivery of materiél, which can be 2000 tonnes per mile.
Whereas if the steel rail is lifted, it's $2 to $3 million per mile to blaze a new railroad on an old grade. Including double transload of most of that materiél. That's so expensive that I can count on the fingers of one hand the number of times it has happened.
Much worse, many abandoned railroads are vulnerable to reversion - rather than buy the land outright, the rail company bought an easement conditional that when the railroad goes away, the land goes back to the underlying landowner. That means the right-of-way itself gets busted up; now you've got an apartment building on the right-of-way, and you'd have to buy it and destroy it to put the railroad back in.
Here's a success story: the Susquehanna Railroad. Their operations shrunk over the years, and part of their line was disused. Some motorcar collectors got permission to cut the trees growing up in the track, using the motorcars to get access. Their real goal was to have a place to ride their motorcars! As business at the Port of Newark grew, there was an opportunity to run massive container trains (instead of trucks). So Susquehanna evaluated whether that was feasible. They rode the line - in a motorcar - and were able to rehab the line cost-effectively because it was passable. Very nice save.
Bottom line: Once the rails are lifted, they never go back down.
So when you see weedy rails, think "Thank God those are still there".
Now, the government is doing several things to help. First, they are buying up defunct rail lines, and keeping them "rail-banked" for future use. Many a heritage railway sets up shop on such a preserved line. Second, they're agreeing to tax disused rail lines same as abandoned ones - so there's no financial incentive to lift the rails. And third, Rails to Trails is allowing the rights-of-way to be captured whole despite reversion clauses, for use by biking trails, pipelines, roads or indeed railroads. So no more apartment buildings on the right-of-way.
Part of Rails-to-Trails allows rights-of-way to be reactivated into railroads again. Again, not likely, but it holds the door open.