If you pay someone to make a chair, you don’t deduct the salary. Instead you create an asset valued at what you paid to build it, then depreciate it over time.
The arguement for this is that it would be inconsistent to do otherwise. After all, why should buying a chair from someone else be different than paying an employee to do it?
It’s worth noting that this change brings the USA in line with international financial reporting standards, so it’s not like it’s some crazy unique idea or anything.