I believe that person who bought bitcoin 5 years ago had already sold their bitcoin  back in 2017 when they Kept the Holding for 2 years and that should be a Multiple value from the time of Buying so who would still Hold when you have already gain too much amount?and even if you wanted to hold for long yet you will take the advantage of selling first then Buy again in cheaper price because that year bitcoin has been proven to go upside down so practicality wise to sell High then Buy Low.

and also you are correct that those wallets that still holds bitcoins for that long might have been a dead wallet meaning keys cannot be found anymore.