If we are to talk about the privacy their are also some Altcoins which are privacy coins like the monero it’s a good option for anyone who want to hide their privacy, another reason why other can invest in Altcoin is for cheap and fast transaction, look at what was happening in time of bitcoin network congestion the pressure was moving to Altcoins which where used for as alternative for transactions just as they are supposed to be Altcoin (alternative coins).
You gave an instance of when the price of Bitcoin transaction fees was high and people start switching to other options especially business owners who recieve through cryptocurrency. Now that the trauma is over everyone has moved back to using bitcoin. Altcoins are unique because they are always available when you need them and you can have multiple choices when you want to invest in them.