I see no reason to sell BTC now, when its price is not high and halving should happen soon. Moreover, the popularity of Bitcoin and other cryptocurrencies is constantly growing. Now is a good time to buy and increase the volumes of BTC and altcoins on your wallets, but you need to decide on the budget allocation in order to understand what percentage of BTC and what percentage of other coins you will have.
I see plenty of reasons to sell.
Just because people are Bitcoin believers and hodlers does not necessarily mean they never sell,,, for example if you mine bitcoin or you earn it, then all your income is in bitcoin. If you can pay directly for btc for bills and rent and food, great. But until today I have not found a supermarket accepting btc, or phone company doing that or landlord in my country taking btc.
Reality is you still need to sell btc for money in 90% of cases.