Locomotive sanders removed

Does anyone know a specific reason why most older locomotives that were originally built with 8 sanders now have their additional trailing sanders removed? Is it purely a maintenance/expense issue that older locomotives in local and secondary service don't require 8 sanders or is there another reason? I have noticed this among Class 1, regional/short line, as well as export locomotives. But it seems many roads that removed the trailing sanders on older locomotives have continued to purchase modern road locomotives with 8 sanders, so it seems that 8 sanders are still preferred on the newest road power.

I have noticed that sometimes the inboard sanders on each truck are removed. Guilford did this on many of their engines. The piping is still intact, but the hoses are removed, and the magnet valves are unplugged, or even missing inside. They also removed the center windshield wipers. In their case, it is likely to skimp on maintenance. Once RMC had an article about GP60s. They had drawings of SP, and ATSF units. One or the other didn’t have sanders on the inboard ends of the trucks.

FRA requirement is only to have sand on first powered axle .
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At CSX we inherited a lot of Dash 2 Locomotives from Conrail. The Conrail Units were good units but a large number of them did not have intermediate sand. My point is that when Track Testing these units against another units, you could tell a big difference in the operation of the Locomotive without intermediate sand by monitoring the WS10 module pins 8 to 21. The units with intermediate sand will run a much lower AC voltage at pins 8 to 21. The lower the voltage, the better. When you see 30 VAC at pins 8 to 21 you have entered 2nd stage Wheelslip and the Red "LED" will come on for 6 to 8 seconds on the SA10 module trying to correct the problem by sanding automatically.
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As noted, federal regs require sanding on the lead axle. They do not require it on the inboard sides. HOWEVER - the feds have a policy that "If it's there, it must be functional". So to simplify maintenance and help stay in compliance, some railroads will remove items which are no longer needed or are not required.

Another example of this is class lights. I'm not aware of any lines still requiring class lights. But if they have an engine so equipped, an FRA inspector can demand to see them lit, and if a bulb is burned out or a wire disconnected, that's a defect. So the common remedy was to remove the lights, sockets and lenses, and weld a steel plate over the housing.

Carrying that to an extreme, I heard a second-hand report of a museum which had an E unit they wanted to use in excursion service. Pulling only a few cars at low speed, they figured the one functional 12-567 would be adequate. Reportedly, an FRA man nixed its use, since the second prime mover was still in there and was not functional.