It would surely just gonna depend on the reason of the holder but there are sure many different reasons behind it, but I would probably say that a high percentage of those people are doing it for profit or money.

I mean there are people that doesnt have any plans on selling their Bitcoin until they die which is almost similar to religion at some point, maybe like Bitcoin believers, but if they dont want to take profit from it, that just means that they dont want the money on it, probably status, standards, etc. Since having or holding a huge amount of Bitcoin could be a title probably.

I have some friends who don't have any plan on selling their Bitcoin investment just because they are going to use it as an inheritance for their kids or something like that which I think is going to make more sense.

Personally, I'm holding Bitcoin just as an investment to make a profit, so I keep on accumulating Bitcoin, probably going to sell if there is a good opportunity in the market, after selling and making a huge profit from it, just going to repeat that cycle again probably buyback when the market is down again to create more and more profit on it. I dont really see Bitcoin as a digital currency at this moment since the market is just volatile it's not really fit right now, but I think it's fit as an investment, and for sure a lot of people are doing it because of that reason as well, but in the end there was no right or wrong about it it is still going to depend on you how you're going to see buying Bitcoin on your perspective.