maybe because bitcoin is virtual and they are afraid of being scammed. people put their trust on the things that is visible to them and living its worth since then.
Both are not to be compared. Both have their own characteristics and both are giving their own benefits. If we talk about price then gold has a stable price and is accepted all over the world while the worth of bitcoin fluctuates and is not accepted everywhere. People are favouring both.
If we talk about investment then gold is lengthy process and is needed to be converted to paper money first and when it comes to bitcoin then it is quick to be transferred and gives a high output. It has brought the world to a single platform through internet