CMC and coingecko both very useful for us, i used to use both however i am confused why many coins and tokens not listing in CMC but listing in coingecko, not only coins and tokens but also many exchanges, is this because coingecko become more popular than CMC, or for something else.
No, CMC is almost most popular one. Less tokens/coins are listed on CMC because the conditions are a bit heavier. Look at the listing criteria of CMC:
https://support.coinmarketcap.com/hc/en-us/articles/360034124351-Listings-Criteria It will be more useful to use both. There are shortcomings, such as false volumes or listing scam projects, but this may not sometimes be caused by themselves.