Exactly this. Go and look at any of the heavily shilled coins from the 2017 ICO craze. Or any of the heavily shilled coins from the IEO/ITO craze. Most of them are dead or dying, down >99% from their peak, little to no ongoing development, no real world use. We can already see the same happening with some of the coins from the ongoing DeFi and NFT crazes. Let's check back in a couple of years and see where we are. I guarantee 99% of these projects will be dead, and bitcoin will still be doing just fine. "Diversifying" in to these coins brings huge amount of additional risks for the 1-in-a-million chance that the shitcoin you bought randomly pumps x10. And even if it does, is it enough to offset all your losses from all the other shitcoins you bought?

Buying any does not mean diversification because they are all in the same category - cryptocurrencies. Why take the risk with a random altcoin which is far more likely to drop to zero than it is to make any real gains, when you can just stick to bitcoin. If bitcoin dies, your altcoin dies too. If your altcoin dies, bitcoin doesn't care.

With hindsight, you could be rich by buying and selling Bitconnect at the right time. That doesn't mean it was a good coin, or has good technology behind it, or has a good team behind it, or has ongoing development, or has a real world use, or belongs anywhere near a smart portfolio. Betting on random shitcoins like these is a gamble, not an investment strategy.