It's supply and demand and many other factors. Value of houses can very easily change. To illustrate, imagine a mini-economy, where there's a village. Each person in a village has their own profession, they don't have currency, but they do trade their produce with each other. Just as an example of how a value of something can change.

Let's imagine there's 30 families or just maybe 30 people. Let's say there's also 3 people who build houses. Now they keep building and since each of those people needs a house, they are willing to give some of their produce to the builders. Now at some point, all of sudden there's 30 houses built.

If they build another house, what will be the value of this house? As all people already have a house. But this house is identical to all the other houses, shouldn't it still have similar value and shouldn't builders be getting the same? How will builders make anything of value for others to be willing to trade some of their produce?

And actually, you could in a way solve this problem if this village adopted currency of some sort. Builders could instead of asking produce which might expire in few months, ask for money and ask enough money that by building all of those 30 houses, they will be covered for life and never have to build another house.

And if it would happen that builders suddenly lost their capability to work after building 15 houses, what would happen to the values of those houses? Everyone will need a house to survive, so everyone would be willing to offer whatever they possibly can.

A reason why economy might be cyclical is that while trying to organise all the logistics of what gets built, supply, demand and all that things can tip out of balance.

And I'd like to say, whether economy is artifical, social construct, it optimises and helps organise people. Without money you'd have hard time trading, logistically, keeping track of everything. And without banks or loans you might never be able to own a house or start your business. All of these things and economy benefit the society as a whole, it's just that sometimes things can go wrong, but it doesn't mean that we are worse off after things go wrong than we would be without economy.

You can easily see from those basic and primitive examples of how economy will make life easier/better for people.

You could construct modern economy out step by step, how economy came to be and it should give you understanding on how each of those steps solved a problem, helped society grow or just benefit people and make their lives easier.

You can start on the personal level and ask a question:

1. Why can't I just exist alone in the wild? You can, but it's very possible you get injured by a wild animal, are unable to hunt for food and simply die from a very simple injury very early in your life.

2. Okay, sounds like it would be better to cooperate with people, so if one gets injured, others can help out meanwhile. Also this would allow for some part of the group to focus their time on one activity like hunting so they would get as good at it by experience as possible. Someone else in the group could deal with helping people with injuries, so they gather experience there and will be better and better as future comes along.

And so on and on... You should understand why economy is important once you have gone through all the steps.