Huh? Welcome to 2018, lots of people have 10Gbps at home. I'm connected to my NAS over 10Gbps and it makes it act like it was local drives in my PC. The bonus is that I don't need to sit and listen to the spinning rust noise. Yes, 10Gbps is still costly, hence why 2.5 and 5Gbps is happening, although at least for now, 5Gbps isn't really much cheaper than 10Gbps.
With Realtek stepping into the 2.5Gbps arena means that we're going to see sub $10 costs for 2.5Gbps and as pointed out above, it runs over normal Cat 5e cables, so no need for fancy cables to make it work, unlike 10Gbps.
Why wouldn't you want faster Ethernet? No-one backs up over their network? Copies files? Or is everyone really using Wi-Fi and that's it? I would go crazy if I had to put up with Wi-Fi speeds for backups.
This is NOT a marketing scheme, it's a real thing and it has tangible benefits for most people. No, it's not going to improve gaming, no it doesn't require a faster internet connection. It will require faster switches/routers though, which is a downside of it, but it still works with Gigabit hardware. There are no downsides to this, only upsides.
But hey, let's only make things that are just good enough to what we need today. Why bother trying to improve things? Let's go back to coal power and two stroke engines while we're at it, or why not, steam engines...