Investors are skeptical about altcoins since many of them are not as decentralized and censorship-resistant as Bitcoin is. Aside from the fact that altcoins' prices are much more volatile than Bitcoins', most of them are still in experimental stage. Investors can expect altcoins to be an unreliable investment compared to BTC. Despite the inherent issues of alts, it's still possible to make a profit if you know how to play your cards right. Altcoins are usually driven by hype, so they could rise astronomically in price for a short period of time. But don't expect to take them seriously as a long-term investment because of the reasons mentioned before.
Picking the right altcoin is a hard and time-consuming task. I'd stick with Bitcoin and Ethereum for complete peace of mind. As long as you invest wisely, there should be nothing to worry about. Just my thoughts

But, there are many people who buy Bitcoin and use it for investment purposes only. They don't care about Bitcoins decentralized factor. The main reason why many people are skeptical about Altcoins is not because Altcoins are more centralized but because most of them are just scams.
When it comes to volatility, I think it was Bitcoins are the ones who are more volatile because it is less regulated. There are old Altcoins like Ethereum and Litecoin. They are not on the experimental stage anymore. These are the Altcoins that we should invest if we want to diversify our funds or if we are simply bored on investing in Bitcoins alone.
I believe investors are full of doubts about what altcoins to pick, because they want to be sure to choose the one which is going to return huge profit percentage to them. However, they ignore the fact nobody can predict such hypes, since it's heavily lead by sudden speculation created by whales in an attempt to manipulate market's prices, executing their pump and dump schemes.
With few exceptions, there aren't strong factors to consider in order to explain why one altcoin is performing well, while others aren't.
Consequently, for doubtful investors, it's highly advised they put their money into bitcoin to minimize losses and care for the investment's safety.