I bought altcoins compared to bitcoin because I saw the possibility to skyrocket greater than hold bitcoin, as we know that the price of bitcoin is already expensive while currently many altcoins are very cheap even if we invest only $ 10 then the opportunity to get big profits because new coins are usually will burn or pump big.
This doesn't really mean that you have to hold either the one or the other. I mean I do believe that alts have a better chance of skyrocketing to a higher price but that doesn't mean that I will not hold bitcoin neither. So, I have some of my investment in bitcoin and some of them in other coins and they combine to be a good portfolio. I have been in the green for a few years now, not super rich or anything but doing alright for myself.
I assume this will be the case for a while longer. This is why if you think bitcoin is safe, then spend a little on alts so you do not lose too much, if you think bitcoin is TOO safe then invest a little bit to bitcoin so it is still safe there.