A lot of people always recommend to diversify your investment. Beside Bitcoin there are many altcoins which have potential to become more popular in the future which would cause their price increase. I keep most of my investment in Bitcoin because it seems to be the most profitable right now. I usually try to look for the best time to buy a certain altcoin instead of buying every I wanted in the same time. I always try to hunt for bargains. Going all in Bitcoin is a good idea only if you don't have much money to invest
Diversification is recommended because all other alts that cost close to 1000 dollars, some of alts crossed that mark already. When you look at the past when prices of that alts were less then dollar, you can see that many people made a very high profit on that alts.
Bitcoin price will grow, ethereum price will grow, neo will grow, but I'm sure that many alts that now cost less the a dollar will grow too, not all of them of course some of them are scams, but that is our job as investors to recognize true potential of alt before we invest some money.
Just had core people invest only in bitcoin, I think many others will have higher price in the future too. Nobody can say nothing for sure, entire market will grow and why not to have some from all the ones you like and find attractive for investing.