In the early days of SSDs, they were so expensive that most people ruled them out just because of the price tag. Performance wasn't great at first, but then came the Intel X25-M, followed by a bunch of SSDs based on the Indilinx Barefoot controller. By the end of 2009, there were a number of good SSDs on the market. SandForce would launch a good, new controller the next year, and later Samsung, Phison, and others would figure out how to make a good SSD controller.
I bought my first SSD in 2009. It cost $300. It was 120 GB, which means that the Windows installation alone needed a considerable chunk of it. And that was a good deal at the time. The same price tag for an Intel SSD would have gotten 80 GB. There were larger SSDs, but for most people, even if you bought an SSD, you'd also need a hard drive to get the capacity you need. The SSD was an extra expense, not a replacement for a hard drive.
Fast forward a decade and things have changed. Let's look at New Egg pricing, and restrict to new drives sold directly by New Egg. For hard drives, that pointedly excludes some refurbished "White Label" drives, as well as some very old models sold by EOL Tech. After all, if you're buying a drive that is going to be your primary drive for a computer, those are really not what you want.
The cheapest hard drive available on New Egg is now $38. That's not the cheapest of some particular capacity. That's the cheapest of any capacity, and without regard to speed or form factor. The second cheapest is $43, and it goes up from there. That's a 500 GB drive, so it's pretty small as hard drives go.
The cheapest SSD on New Egg is $22. That's a lot cheaper than the cheapest hard drive. If you just need some cheap drive that will work, an SSD is actually cheaper than a hard drive. The reason is that you can't make a working hard drive with fewer than one platter. Having all of the mechanical things in place to make a working hard drive with one platter costs a fair bit of money, and that's as cheap as they can make it. But you can readily make an SSD with fewer or lower capacity NAND chips. A PCB, an SSD controller, and some other bits cost money, too, but it's a lot less than the basic cost intrinsic to building a hard drive.
Now, that cheap SSD is only 120 GB, which for most people, is just not enough. But you can get a 240 GB SSD for $27. That's still a lot cheaper than a hard drive, and for a lot of people, that is plenty of space. That won't be enough for a lot of gamers, but still, for a cheap desktop, it's actually cheaper to use an SSD instead of a hard drive.
If we insist on 512 GB to roughly match the size of that cheap hard drive, then the cheapest SSD is now $40. That's only a $2 price premium over a hard drive. And half a terabyte will be enough for a lot of people, including a lot of gamers. That's what I've got in my desktop, for example.
That means that we've now reached the point where there's really no case at all for buying a hard drive unless you need more than half a terabyte of capacity. As capacities go up, hard drives can be more attractive, of course. The costs intrinsic to a hard drive with a single platter don't change much if you make that single platter much higher capacity. Thus, you can get a 1 TB hard drive for $45, or 2 TB for $55. Both of those price tags are available from either Seagate or Western Digital.
But reasonable storage capacity needs for consumers haven't scaled up nearly as fast as hardware capacity. If it had scaled like hardware, doubling every two years, that 30 GB large game installation a decade ago would be closer to 1 TB for a game today. It wouldn't surprise me if there are games that need over 100 GB, but I'm not aware of any. A lot of games, especially low budget indie games, are only a few GB, or in the low tens of GB. So that 500 GB of capacity today is about as likely to be enough for you as 240 GB was a decade ago.
But even needing a lot of capacity doesn't necessarily mean that you need a hard drive. You can now get a 1 TB SSD for $80, which is nearly the same price as getting 1 TB in total from a hard drive and SSD combination. If you need 2 TB, you could get two of them for $160, at which point you're finally paying a meaningful premium for SSD speed. But 2 TB is a lot of space, and that's still not that expensive.
So you see why Western Digital and Seagate are concerned about the hard drive market mostly going away. Western Digital has gotten into the SSD market via buying SanDisk, but they're not nearly as big of a player in the SSD market as they have been for decades in hard drives. Seagate has some SSDs, but they're just one of many partners buying and integrating a controller and NAND from other vendors.
For years, most people needed a hard drive rather than going SSD-only just because of the price. That argument has been diminishing in potency for a number of years now. Today, for most people, it should be gone.