Whenever people need fiat they will sell their bitcoins for sure, but may be they are selling in installments and not all of their bitcoins, so only holding is not profitable in long run, you should keep on spending your coins.
Most people are doing this,just when they needed and for emergency purposes but not all coins.Bitcoins has great potential as time passed and I think its much better to hold for some time. Monitor and observed also this coming halving.
I hold some bitcoins in separate wallets which are meant to never sell. It's for the really long long term. And i am sure some people sell coins to pay for bills but at the same time they hcoins for the future.