Re. 'maintains its quality' aka, the good stuff.
What is the most important source of natural gas? Coal, oil or other?
"Above the maximum temperature the oil is converted to natural gas through the process of thermal cracking." "with nothing acting as a capstone it [will lose, and will continually lose], all its gas."
If it's already 'cracked', it has to be transported in a gas tanker, instead of sludge that just sits there. And if there are any cracks (permeability of the container), the most volatile and profitable constituents are lost.
A barrel of crude oil can be converted into 47% gasoline, "20% is heating oil, 8% is jet fuel, 18% natural gas" and 7% : "the rest being coke, greases and asphalt". – Could I make money off of the negative oil price?
If it 'cracks' bad enough and leaks, you're left with the sludge (heating oil, coke, greases and asphalt). And the more it cracks into tiny gas molecules the more it's going to want to leak. And the more it leaks the less your profit margin.
Too cold and you can't pump it. Too hot and it cracks. It needs to be just right. Because if you're not shipping me (the good stuff) crude oil that I can turn into 47% gasoline (and all the rest, especially that 18% of natural gas), then I'm going to buy it from someone else.
From Ward's answer: promoting circulation inside the tank "reduces sedimentation and wax formation." - Sediments don't pump very easily and no one pays $4 a gallon for wax. I don't know how much it costs to turn wax back into the more profitable thing that it once was, or even if that can be done economically or at all, but I rest assured it costs more money than keeping it 'hot'.