For a company, you have much more influence on what happens to data with Nextcloud. You don’t depend on specific hardware (you can upgrade or change it), the software does not expire, … and you should have the experts that should know how to set it up. The nice thing about the commercial NAS solution you buy the hardware and can easily set it up, with Nextcloud it is a bit more difficult (Nextcloud Pi should make it not too difficult in combination with a Raspberry Pi, but you need to buy it and an external drive).