Bitcoin is not everything , you can still have a good portfolio without it.
Why add Bitcoin now? It maybe 2x this year from current price and will then spend the next 2 years after that going down in bear market.
Altcoins in the current top 100 or so give you a good chance of making very good money this year, Bitcoin doesn’t.
Yes, bitcoin is not the only investment on the market, nor is it the only coin worth investing in. But it is the safest coin in the market so we should have bitcoin in our portfolio, although it may not give us big returns like altcoins but it will ensure the safety of our portfolio. But it all depends on each person's taste and risk tolerance and remember that the higher the return, the higher the risk.
If you are willing to take risks and would rather gamble than invest, then there is nothing wrong with not adding bitcoin to your portfolio. But this is very risky so don't give altcoin investment advice indiscriminately to others.
Maybe the apparent confusion can be resolved by differentiating investment portfolio from savings?
To folk whose savings are in fiat, as often happens with people whose earnings/income is fiat, bitcoin is in their minds part of their investment portfolio;
whereas to at least some folk whose earnings/income is bitcoin, bitcoin is simply their savings as in what they haven't yet spent of their earnings/income at any given moment, except maybe such bitcoin as is out on some exchange or other as buy-side for various alts invested in to act as support for those alts and to earn from the rises and dips in the BTC/ALT pairs...
-MarkM-