Fuel tank rust perforation.

I had to replace the fuel tank on my '97 Lumina 3.1 150k miles as it developed rust holes 1/4 inch above the pinch weld in the back where the weld is bent up some to allow for the straps. Apparently this area holds
road grime (and moisture) quite well.
Symptoms were a fuel smell, yellow stain on the tank exterior, plugged fuel filter, fried fuel pump, high long term fuel trims under load (+19.5%), and a bad surging misfire when first restarted hot that made my aftermarket tach swing between 500 and 1500 RPM about 3 times per second. Revving the engine once usually cleared this up but then it got worse to the point that when put in gear the RPM fluctuated so rapidly it made the serpentine belt chirp and a couple times even caused a flashing MIL and a P0300 random misfire code. Oddly no EVAP leak codes were present. This is per an OTC 4000 Enhanced scan tool and the Pathfinder '96 software.
Post mortem teardown inspection of the pump revealed that it was made in '03, the commutator was fine, but the copper flex wire from the positive terminal to the carbon brush was completely gone so the current had to go through the spring instead which acted as a resistor and slowed the pump down and the heat both made the spring lose its tension and discolored the plastic top of the pump around the terminals. I can't believe the pump assembly costs over $300 new.
For now I have in a salvage yard tank and I cleaned off the surface rust in the areas that rusted through on the other tank and smeared on some good grease to hopefully protect the metal. I plan to install a new tank in the spring.
My question is why if a '91 Caprice 9C1 (with approx 300k miles when junked, VSS went bad along with the cluster) can have a plastic fuel tank why is the Lumina's (thin) steel?
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Daniel who wants to know wrote:

Consider electrically isolating the straps from the tank with strips of plastic. It may stop the galvanic reaction or slow it down. The pump and sending unit should have their own wired ground, oem.
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The OE (not OEM) straps are plastic coated already. The whole assembly plugs in via a 6 pin connector. Pins not in any specific order:
Pump power Pump ground Sender/FTP ground Sender signal FTP +5v power FTP signal
FTP= fuel tank pressure sensor.
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