I am one of the many that did a mistake that have exchanged my bitcoin for some alts. Those alts that I've purchased became zero and forgotten.
Whilst for Bitcoin, it is still there and making rounds globally. The amount of money that I've wasted for doing that is regretable but I can't help myself but just to learn from that mistake.
And so, if others are still moving forward to having bigger portion of their holdings in altcoins. It's their choice to make, but us that have been here for a long time, we know what to do and what's the most important thing to hold today and for the next years to come.
That wouldn't happen if you converted bitcoin for ETH or dogecoin at that time, and you would even made more profit than holding bitcoin if you had held them until now. Because as I remember, ETH price in 2015 was only 1$ while doge average price was 0.0001$.
I don't recommend people invest in altcoins because it is significantly riskier than bitcoin, but it is clear that not all altcoins are the same and they will all disappear over time. There are a lot of altcoins that were created 10 years ago and they are still around and growing today.