Unfortunately the way that the railways are maintained today results in both new rail being left for long periods out on the track, and used / old rail, sleepers and other removed equipment/items being left for sometimes many, many years.
It’s not normally a risk to trains. But it does make the railway an even bigger tripping hazard for staff, including maintenance staff.
It can (depending on what it is and the size/length) also be ready supply of ammunition for vandalism.
Rail left in the four foot can also travel in the direction that trains move, and then damage signalling cables, OHL return bonding wiring, AWS equipment, TPWS equipment or ATP equipment.
The reasons for new rail being left in the four foot are normally due to a rerailing programme having been postponed or cancelled.
The reasons for everything else (scrap) is that either it was not planned to be part of the renewal project. It is planned to deal with the scrap at a later date. The occupation time was too short. The 360 / road-rail machines broke down. Or resources were diverted to attend a defect or more urgent work.
There used to be a scrap rail recovery department with its own specialist train. But this was closed some years ago after an accident. The cost of the retraining made it uneconomic to continue given that the local maintenance departments were using this service less and less. Preferring to do things their own way... (or not as the case may be).
With a lot of projects, it can take years for all the redundant or scrap materials to be removed.
The poor state of the line side and the cess, is something that the union representatives and the staff have been complaining about for more than fifteen years. The answer we often get back is either, that it was not in the contract (when a contractor has done the renewal work), or that there is no money currently available to fund a tidy up or improvements. Although mainly this is referring to the cess path having been destroyed or covered with loose ballast or spoil and the company being unable to, or unwilling to put a cess path back in.
Occasionally, the company will actually have T3 occupations purely for scrap recovery.