Why? This is not a one-off cost. You wouldn’t be paying for a product that you bought once and can be used indefinitely. Software needs to be maintained, data needs to be stored, bits need to transported, mods need to be paid for their ongoing work, etc.
Mind you, I am not talking about price levels of a Netflix or Twitter Blue subscription. I am talking about a much lower price point. $10/year would be more than enough for me to make hosting a large instance a sustainable venture, which would even let me keep my pledge of giving 20% of the profits to the development teams of the upstream projects.