bitcoin now is very popular in the world so. many coin appear just make bitcoin prices go down
No, the great number of these new tokens will never affect Bitcoin's price. Vice versa, BTC can become even more popular and more expensive. Many of the shitcoins will die.
The number of altcoins will not be a threat to bitcoin because bitcoin has become so popular. Every time we talk about crypto currencies, the first thing that comes to our mind, mostly, will be bitcoin. And the reality on the ground to date, even though there have been a lot of altcoins out there, bitcoin remains at the forefront.