As someone who has worked in several crypto companies and exchanges, I feel I am specifically qualified to give some insight here.

There can be a number of reason as to why one would do this.

'Whitelabeling' is basically being able to use the technology of another company, which in this case would be their exchange engine. However, when whitelabeling, the creator of the technology allows the other company to use its technology WITHOUT the branding of the other company. Basically, I have an exchange platform. I can build one just like mine but for you, and we call it your platform. Same technology, different owners.

If you would love to have a free 15 min call to discuss your idea in further detail feel free to message me and I will send you a free link