The main reason to invest in bitcoin is because of its popularity that already made it the mainstream of cryptocurrencies. Although it is very risky investment, it can also make your investment doubled or tripled in just a short period of time.
While its risk is better to take than any other altcoin that you don't understand if they have use case.
But I would disagree with the double and triple part you mentioned. As of now, there's no guarantee for that because we're still in the bear market and like today, the market is so reddish and that's sore in the eyes again of most of the holders. But as long you trust bitcoin and believe the technology that it brings, you're doing the right thing of investing to it.