Yes, this is actually not unusual. People need food, water, shelter, and suchlike in order to survive, and so they exchange their labour for goods and services. Money is a helpful token now rather widely used in this bartering process.

I know it's quite common in the web development community to take a lot of freely provided code which took immense labour to write, and then stitch it together, in a way that requires very little skill or effort, in order to sell the result - but this isn't the norm in the world at large.

Their developers decided donating their time to a bunch of demanding know-it-alls with no appreciation for their work was a bad deal for them.