Many of you may not be familiar with the existence or the reason of Ethereum Classic (ETC), to give it to you short, some people wanted to create the first big DAO on Ethereum, raised an unbelievable amount of Ethereum and $ at the time for it only to find out there was a bug in the smart contract which was allowing a hacker to steal the coins at a rapid pace. Upon finding out about this the Ethereum team quickly contacted mining pools and asked them to halt the blockchain, this was a very controversial decision as a blockchain was meant to be immutable.
Bitcoin maximalists of course were having a field day, forgetting all the bugs and times Bitcoin had forked or had to be halted and patched up and were instead pointing fingers at Ethereum and the teams decision to do something about this hack. To them it was an obvious choice, it's the investors own fault for not having seen this coming and they should not compromise the integrity of the blockchain to save them. Luckily the Ethereum team did not see it the same way and figured if they could, they should help all investors get their funds back, so they rolled back some blocks and transactions and forked the hacker out.
Through all the controversy and drama some users felt the need to create a copy of Ethereum called Ethereum Classic where the fork of the hacker never happened but the immutability and integrity of their clone was intact.
To many this seemed like a stupid thing and everyone was baffled as to why ETC was maintaining a high price at around 10% of the marketcap of Ethereum.
A couple years later Bitcoin forked and created Bitcoin Cash, this was quite different and even though I'm butchering these short explanations and possibly leaving out a lot of important facts or adding things that I may remember wrong - it also managed to hold a safe position at around 10% of Bitcoins marketcap.
What does this percentage mean?
I realize that not many may think about it but it is quite simple in a way. It's basically a prediction market. Combined with the forks having granted initial holders of the original "new" coins, many did not want to risk the odds if this fork were to surpass the original in one way or another.
Of course for Ethereum it did not effect them a lot, they continued doing their thing and improving from there and did not care about the forks existence. One could argue that if ETC did not exist ETH would have had that percentage on top of it instead but that is impossible to tell and due to reasons like receiving free coins and holding them with no risk and at the same time many of the addresses probably never even touching the forked coins it gave a lot of leeway for the marketcap to exist just because of the amount of coins and low liquidity of circulating coins.
With Bitcoin Cash it was quite different cause it had a much bigger psychological meaning to it and what it was striving to do, it was not just because of immutability and integrity of the chain, it was more about the goals of Bitcoin and the vision of Satoshi they felt the people in charge of Bitcoin now had deserted.
To get back to the title, the percentage of the marketcap does not always mean "that's how much money has been invested into that coin". It seems many think when the marketcap of bitcoin rises with $3 B that means $3 B fiat just entered it. This is almost never the case, think about how many holders are holding long term, cold storage and almost never keep their coins on an exchange. It only takes a fraction of the daily volume to move the coins up and down by millions if not billions.
When it comes to forks and comparison to the original, if ETC is at 10% marketcap it may not mean that people think there is a 10% chance that ETC will surpass or catch up to ETH's marketcap. There is a lot more to them than just that.
Same thing can be said about "dead coins", a dead coin can easily mantain a few million in marketcap, it may never go to 0. I remember a lot of people were looking at Steem when it went all the way down to 7 cents and were like "yep it's dead now" and on second time around when it was nearing 20c last year they thought the coin was dying and didn't touch it only to find out later again that they missed out on the best buying opportunity of possibly the rest of its existence.
A coin is only dead if no one is trading it, if there is no one buying it then no one can sell it. If no one is buying or selling it, the exchanges will want to delist it. That's when a coin dies.
Just something to keep in mind for the next bull market and if you're scanning through shitcoins on coinmarketcap trying to find a couple gems. :)