Depending on what you want to pay, what hardware/platform you want to use, and whether you're concerned about open source and other licensing, there are several options for NVR.
I've only got minimal experience with Zoneminder but I've used iSpy (https://www.ispyconnect.com/) fairly extensively running on desktop computers and, later, on an old laptop repurposed as a NVR.
Later on I started using the "Surveillance Station" package that came with my Synology NAS. That's closed source and the version I'm familiar with came with licenses for two cameras and the ability to pay to enable more. However, if someone is less interested in extensive setup or doesn't have a suitable computer free for that use, it's a decent option, as are similar packages on other NAS platforms.
I guess in terms of finding a market with adequate demand, the NAS solution would be a good one. There are already models that are geared and pitched toward use as network media servers. I'd be curious if one of the bigger NAS companies might come up with a model that's targeted as a NVR.
The cameras are cheap and plentiful enough but many current consumer-grade network cams are either sold as "cloud" only or involve lots of potential security issues. Several offer DDNS routing as a way to check your camera feeds from outside the LAN but don't adequately explain the risks in opening a port to a device that may have several exploits available. Others tout their easy setup and compatibility with mobile apps but neglect to stress that you need to access them via a desktop application or web interface on a non-mobile computer in order to see the security settings, change default passwords, or otherwise configure them properly.
The end result is thousands of network cameras easily accessible to anyone with the right Google or Shodan search terms. Restricting a device to "cloud" only may solve these issues for many people who would rather pay a monthly fee to let someone else handle their data but I think there's a place for something in between.
A basic NAS with some storage and software similar to what we've mentioned offers the ability to connect multiple network cameras, store and manage recordings locally, keep actual cameras inside the LAN with no outside access, and also serve as a location for home backups and file server duties.
I'm honestly surprised that a hardware-oriented company, whether a NAS company or something more like Apple, hasn't marketed a line of simple home NASes with IP cameras as additional options for purchase. By selling their own branded cameras they would get more add-on sales from people preferring to get everything of the same brand and more enterprising users could easily add their own IP cameras as long as they use one of the common protocols.
It's nothing you can't set up already but people seem to like turnkey systems and I'd imagine there's a segment between "just pay a monthly cloud subscription and forget about it" and "I'll just set up this old PC in the closet and configure some open source NVR software".
I guess the question is whether people would even bother since the initial cost is higher than some Dropcams or even a dedicated CCTV system like they sell in electronics stores.