I'm not sure if they do, but now we have the double requirement of getting everyone to use I2P and Tails just to use this messaging service. Kind of a nonstarter. Yeah, VPSes are often too small, especially to run relays with the conntrack limits. The other problem is the host OS can see what the VPS is doing. Even if you rent the VPS anonymously, you run the risk of the provider noticing you're doing something illegal and canceling the service or notifying LE. On the other hand, a lot of people can't afford multiple dedicated servers for physical isolation, or it's just not worth it for them. While physical isolation is better, one dedicated server with some VMs is still way better than running naked services over Tor, and it's within more people's budgets.