A lot of reasons, learn and never invest in altcoin and abandon it and say you will come back in the future to cash out millions, you might just return in the future and discover there is no longer a project associated with the altcoin you bought.
If you must be Away for even a day in this space, Buy Bitcoin instead.
I completely agree with you, since a year ago I encountered a lot of reasons why some of the altcoins I was holding and had a good price value fell below zero due to the reckless teams of these altcoins who made quick decisions from changing the coin contract, merging it, transferring it to another network, or The exchange platforms that listed these altcoins have deleted them due to their price volatility, so if an investor will be away from the Internet for a period of a day or more without following the developments and updates and the community of the altcoin he invested, he will eventually get Shitcoins and lose his entire capital, so Bitcoin is the safest investment without a doubt.
I have the same experience since I am the type of investor who buys cryptocurrency then forgets about it and comes back several months to years later. I have lots of cryptocurrency holdings that have gone worthless due to swaps. Others become worthless because of hack and rug pulls. Though I don't keep my cryptocurrency in exchanges, this kind of swap activity done by the developer that has a time frame and needs manual sending of tokens for swap made me lose a good amount of money.
It is indeed true that if we invest in altcoins, we should be always on our toes monitoring them.