Because they are more likely to see that their investment is definitely not going to be a scam. Bitcoin investment in metal product investment such as gold and silver is different. Bitcoin is a digital currency available in many ways, gold and silver have a stable price and price increases depending on demand and supply like bitcoin. More than the bad news that spreads today affects bitcoin so they prefer to invest in gold and silver.
They can be also scammed with those metals. There are 2 things I am thinking while reading the question it is 1st is the gesture on investing to the Physical mining company to harvest Gold or Silver. and then 2nd is purchasing those metals. well Old people are OLD they like old ways and they feel more secure to held the items. that is why they prefer this stuff.