Stamps started off being used to prove that postage had been paid for delivery of an envelope. People collected them. The Post Office then changed the stamps when the prices changed, and people collected them. The Post Office brought out commemoratives, and people collected them. Then the post office brought out multiple sets each year, they brought out first day covers, they brought out year books, they brought out postcards, they flooded the market with product and people collected it. Even countries without a postal service were selling stamps. Then email came out, letters declined, the romance of a letter from a far away place dwindled and collectors were left with a bit of coloured paper with gum on the back which could only be used for a service that few people have any interest in. The collectors moved on to other hobbies, no new collectors joined the hobby and anyone left with albums full of stamps are not going to get a return on their 'investment'.
Phonecards started being used to make calls from public phone boxes (so they didn't get broken in to for the cash). People collected them. The Telecom service brought out different pre paid amounts and people collected them. Then telecoms brought out commemorative phonecards and people collected them. Then the telecoms brought out multiple sets each year, advertisers and businesses put their logos on them, prisons had their own versions and people collected them. Then mobile phones became widespread. No one needed a public phone box anymore and collectors were left with a bit of coloured plastic which could no longer be used anywhere . The collectors moved on to other hobbies, no new collectors joined the hobby and anyone left with albums full of phonecards are not going to get a return on their 'investment'.
Coins started off... well long story short, credit cards and paypal.
We may think that at least we will always have the silver value, I am sure stamp owners thought they would always be able to post a letter with their collection and phonecard collectors figured they would be able to make a call if the worst came to the worst.
The amount of product that bears little relation to the actual original purpose of 'coins' and the decreasing need for physical money means that this hobby is going to finish, fairly soon. I can't get anything extra for my $5 coins, my $1 carded coins have no interest either. I have already spent my '50 cents from circulation' accumulation and I am busy offloading as much as I can so I am not left with albums full of useless scrap metal.
I have a few coins that I like but anything that I am treating as an 'investment' I am getting shot of. Anything that looks like it might only be worth its value in silver I am exchanging for silver bars. Bye-bye Kooks, Koalas, Lunars etc.