When I tell people WordPress is open source, they hear free, and then they get suspicious about what the catch is. Fair instinct. But free is the least interesting thing about it.
The thing that actually matters
Nobody can take it away.
There is no company that can decide to sunset it, triple the price, change the terms of service, get acquired by somebody with different priorities, or pivot to enterprise and stop caring about businesses your size.
The code is out in the world. Thousands of people work on it. If the main organization behind it vanished tomorrow, the software keeps existing and keeps working.
That is not a small feature. For a business that plans to be around in ten years, that is the whole thing.
The counterexample
Think about what happens on a closed platform. A company builds a tool, prices it aggressively to grow, gets funding, gets users. Good product, genuinely.
Then the growth slows down, because growth always slows down. And investors want a return. So the price goes up, or the free tier gets worse, or the feature you built your workflow on becomes an enterprise add on.
Nobody is a villain in that story. It is just what happens when your website lives inside somebody else business model.
What it costs you
Open source is not effortless. Somebody has to update it, back it up, host it, keep the plugins current. Either you do that or you pay somebody to.
The closed platforms handle that for you and that is a real service with real value. I am not pretending it is nothing.
The trade is control for convenience. And plenty of businesses should take the convenience. Just take it knowingly.
The question to ask
Whatever platform somebody is proposing, ask what happens to your website if that company gets bought, or shuts down, or raises prices forty percent.
On WordPress the answer is nothing. Your files and your database are yours and any competent person can pick them up.
On rented land the answer is you find out along with everybody else, in an email, on a Tuesday.