Personally, for me it just doesn't make sense to sell a house or land just to invest in Bitcoin, I mean if you already have it, for sure it is a much safer investment that you have than Bitcoin, mostly these things increase its value over time as well similar to Bitcoin plus its tangible assets compared to Bitcoin which is just speculation, price is just depending on the supply and demand on that market so you have no assurance in the end.
People who sell properties to invest money in Bitcoin barely do it for a security concern but they do it because they believe Bitcoin can generate quicker profits for them if the land or house they are selling has been bought or built for investment purposes. Some would even sell properties that they didn't buy for investment purposes which isn't what I would recommend as you said because it isn't worth it.
For someone like me who is investing and profiting in Bitcoin so that I could buy a house, land, etc., and make it a passive income it doesn't make sense to sell it just to buy Bitcoin, You have a point if it was just an unusable land for you, it's very far away and you just can't do anything about it, it would make sense just to sell it, then buy a new one that is near you where you could actually use, or possibly make an income out of it. Or even live on it, it's a good inheritance for your son and daughters having these houses and land, etc.
Different people will have different mindsets hence different purposes behind doing similar things. You might be struggling to earn some money to build a house, but someone who already has it might think they can earn money by selling it and using the money for investments.
Keep in mind that Bitcoin is still a gamble it is not guaranteed to make any kind of profit out of it, just because you see people get rich on it, it doesn't really mean that you gonna get rich as well, there was a lot of things that you need to consider so make sure you know what you are doing.
Even though I wouldn't compare it with gambling, I would still agree with what you said earlier that one shouldn't sell a property that they know is for use purposes unless they have it as something extra that they might have bought and they aren't using it or going to be needing it in the near future.