The reason they did this is simple. It is cheaper and since the Razer name is more popular among the casual, they are able to capitalize on acting as if they created the switch.
Directly from the keyboard product description "Introducing the all new Razer Mechanical Switches, designed from the ground up for gaming".
To go with the marketing angle, I've also heard rumors that Cherry has been hard to source switches from lately. With their own switches, Razer gets to control its manufacturing chain and production times a bit more.
Although a rumor, this makes a lot of sense.
It still frustrates me when companies rebrand something and call it their own. That's like me making a Gucci belt with the same design and slightly different logo and claiming "built from the ground up and engineered for people who like fashion". It's such a cheap form of marketing and blatantly misleading. It's also in the grey area of legality.
Hell, even their Razer laptop has a case design remarkable similar to the Mac book but in black. They copy and paste designs and try to capitalize on consumer ignorance.
Look at Corsair on the other hand. Even though I'm not a fan of their case designs, they have no problem developing for gamers who aren't keyboard enthusiasts but never hide they are using Cherry MX and give credit where it is due. Then look at how the product quality reflects between Corsair and Razer. Corsair has far superior hardware and doesn't try to capitalize on cheap PR. Sony is another company who focuses more on marketing than delivering a quality product.
The reason this bothers me so much is I feel like this is the nail in the coffin for Razer. I always felt they were going this direction but with this they've completely turned the corner in my eyes. There is no returning from it. First it was when I felt the horrible quality of their $300 keyboard with the LED keys. They called scissor switches "low profile keys for gaming and quick actuation", lmao.
Razer has become the Apple of gaming hardware.