So what I can’t understand is -
Why invest in alt coins if any decline in Bitcoin will wipe out my alt coin profit?
What am I missing?
Thanks
It's not really investing 'twice.' Alt coins are a market of its own. Sometimes, when BTC prices decrease, other alt-coins are increasing in value. Also, Atl-Coins sometimes have a much higher ROI than BTC. Some altcoins go up 50-60% in 2-3 days and BTC can't handle that much growth anymore.
Also, some people are trying to find the next BTC, thinking it will make them rich quick. I don't blame them. There are coins out there that have better technology that tackles the problems that BTC has. Take ETH for example. They tackled the problem of slow confirmations and high fee amount that BTC has. So yeah, it's not really investing twice. Just people being smart with their money.