We use the "character set" our parents and our culture gave us. It does the job as well as any other character set, because language is not merely a tool, like a set of bits for your screwdriver. It's a part of your identity and your place in the world.
You can, of course, pick up other languages and with effort use them either skillfully, or just pragmatically. But no one will ever feel that Esperanto is "their" language. It will always be either a curiosity or, at best, a utilitarian tool (and even then only if it ever becomes wildly successful).
I don't feel English is "my" language, either. It's a language I use, more than my native one, even... but that doesn't necessarily mean I think it's perfect. The point is that its textual representation is lossy.
You can, of course, pick up other languages and with effort use them either skillfully, or just pragmatically. But no one will ever feel that Esperanto is "their" language. It will always be either a curiosity or, at best, a utilitarian tool (and even then only if it ever becomes wildly successful).