Altcoins do have time, the time they have hype, and after that it is gone; if you are among the investors during the hype, you will get huge profit from the project, while if you invested late, you still have to depend on Bitcoin price movement to determine your profit or loss. It is better to from investing in Bitcoin than Altcoins that has already made name.

The Answer you your question “why Bitcoin and not Altcoin” is security of your capital. Bitcoin gives you peace of mind because it is transparent and decentralized, while Altcoins are centralized and can collapse at anytime.