As I also mentioned above, I believe that people will not store crypto assets on centralized exchanges. I just don't believe people who say they don't have accounts on those exchanges and never use them to trade or buy, sell, or convert cryptocurrencies to fiat and vice versa. If we use them for the purpose for which they were created, it is not as scary as many people are spreading it. CEX is a place to exchange, buy, sell, trade...it is never a place for us to trust and store assets. Many investors are using it the wrong way.
The fact is opposite than what you say.
Most of Bitcoin users store their bitcoins on centralized exchanges and even in your post, you mentioned the reason. They want to speculate the price of Bitcoin, want to trade and they store their bitcoins on centralized exchanges.
You can not trade on CEX if you don't store your bitcoin there, do you?
Storing bitcoins on centralized exchanges or any type of online account is bad practice. Furthermore, by trading they will mostly lose their bitcoins with failures from trading.
Reminder: do not keep your money in online accounts.