It is not unusual for collectors to commission artwork from an artist they like.
In these cases, the artist will typically reach an agreement with the customer about what they’d generally like, but the artist still contributes most of the creative effort. After all, that’s why the customer is commissioning the work. In these cases, the artist retains the copyright in the underlying work, but usually will waive the right to sell additional copies, so the commission is unique.
When a corporation is commissioning artwork, it’s usually for a different purpose. The corporation is most likely looking to own both the end result – a drawing, illustration, or photograph – and the underlying copyright.
In most cases, the work commissioned by the corporation is being incorporated into a bigger project – a website, marketing materials, or a shareholder report. By contract, and by the fact that the commissioned work is part of a greater whole, the corporation can say that the art is a “work for hire,” and the copyright is owned by the corporation, rather than the artist.
It’s a best practice to create a work-for-hire agreement, that outlines these facts, and affirm’s the parties’ understanding that the corporation owns the copyright in the work.