Because Bitcoin is not for trading, Bitcoin is for long term investment.
I don't think it's bad for trading, bitcoin also has volatility that is worth trading. Traders can determine their favorite coins to trade after some evaluation. Even on some exchanges you're allowed to use up to 100x leverage, if the Op is good enough at this then he can generate profits bigger or faster than long term investments.
People have different choices for everything. Some use Bitcoins for long term investment, while some use it for trading quick money. But if you want to remain on safer side, then only investing in the Bitcoins will be safe option. We know that Bitcoins are limited in number, hence they will definitely increase in price in long go. So investing a certain amount for long term can give good profits. You always have the option to trade these coins. But if you take risk, then there is possibility that you can face losses also.
Trading is usually done by people in different coins but if one wants to invest in long term plan then he must choose Bitcoin. In terms of trading, other coins in the market always increase quickly due to excess volatility and decrease quickly, so some traders prefer other coins for short-term trading. But if 10 investors were asked which coin is more acceptable in their long-term plans, I think 10 out of 10 would say Bitcoin of course. I myself prefer Bitcoin only for investment but for trading I sometimes try Bitcoin as well as other coins in the market. I can make a lot of profit by trading other coins in the market as well as by trading Bitcoin.