Diversifying is the best way to invest if you ever have been holding bitcoin and you're satisfied with its amount. Due to that, many diversify their assets and chooses to invest into another altcoin because they think that what they're holding right now is sufficient.
correct as the great day of Single investing(holding) of bitcoin have passed long now and yes we are into Altcoin as well now because there are so much happening in altcoins that has been proven over the years.
sometimes Altcoin is even better for short term than Bitcoin.
Altcoins for short term are for real but nothing beats Bitcoin and that's a real thing. If you happen to have a lot of spare money to invest and you're packed already with Bitcoin. That's the time you might want to think that it's now time for you to start buying some altcoins you think are beneficial for you. Not all of them are going to be profitable because as in short term goals of making a profit, you need to be hyperactive at all times because if you're late on it, you'd definitely lose your capital and miss that making profits.