If I'm an Android dev, it might bother me that application suspend is deliberately mishandled on tons of lower-end devices to improve battery life. Should I just ignore those users? If I'm making an email client, it might bother me that Gmail's IMAP support is crap. Should I stop supporting Gmail in my client?
Tools make concessions for the platforms and environments that they'll run in. They always have, and they always will. You get to ignore platforms if you're comfortable saying, "my stuff isn't for the users of those platforms." But so many programmers are on Linux, it probably isn't feasible for most OS projects to ignore them.
None of that means that Linux shouldn't have better emoji support. It should. It's embarrassing that it doesn't. But, you have to deal with the world as it exists today.