I know you can self-host. It's nowhere near as energy efficient as a modern data center with the setups most people have. They were complaining about the power usage of data centers, not realising they are actually the efficient way of doing things. When people talk about sabotaging data centers they are doing it for environmental reasons. Most self-hosters are using shit like old desktops, laptops, or 10 year old Haswell and Broadwell servers businesses don't want anymore. An Epyc Bergamo would give you multiple times the capacity for similar power. Even using new hardware it's normally better to do things at scale as it reduces overhead.

Self-hosting is actually bad for the environment and for your power bill. It's great for privacy, practicing sys admin skills and for breaking the law. If you actually asked people who self-host, like me, they would tell you all this. You can get low energy setups, but you will really struggle to compete against data centers in terms of flops per watt especially if your hardware is running near idle all the time. My electricity is fixed rate anyway, so I don't really care how efficient it is, but I very much know my FX-6300 improvised server is laughable compared to modern server technology.

Though symmetric 1G fiber is quite enough.

How many homes have that? Homes are almost always asymmetric, sometimes to an absurd degree. I have near 1 gig download at my current place, but only 80 Mbps upload. Pretending everyone has 1 gig upload available is dumb, and you know it if you're not an idiot.

Edit: also all ISPs have routers, switches, and servers somewhere in a data center. That's also how the internet backbone works. Large interconnection points, maybe a handful of them in a country like mine (UK).