My son just asked why we don't have a pool.

I said because we don't need a pool.
He said: "Tommy's house has a pool."
Tommy's house has many things. Tommy's dad is a surgeon.
I'm not going to get into an economic comparison like "my dad versus Tommy's dad" with a 10-year-old.
I said that pools are expensive to maintain and that we wouldn't use it enough to justify the cost.
He said: "But we could use it every day in summer."
We wouldn't. We would use it for two weeks, get bored, and then it would just sit there, costing us money.
I've seen the same with our neighbors. They installed a $60,000 pool. They used it constantly for one summer. Now it just exists.
But I can't explain that to a kid who just wants to swim.
So I said, "maybe someday," which is code for "no, but I don't want to argue about it."
He seemed satisfied with that answer.
I'm not going to buy a pool.