Youtube replaced unicode emojis with fucking images
Some time ago, I noticed that youtube comments are copied without emojis, thought nothing of that - bugs happen - but today I finally decided to find out why and what the hell is even this.
Consistency. They don't want to be at the whim of your font (which for many users will be the OS default). While it's not frequent, sometimes Apple (iOS) or Microsoft (Edge) will have a very different interpretation of a Unicode emoji, which makes the UX of comments containing those emoji inconsistent between YT users.
If things work like twitch and they have custom emotes when you 'join' a channel as a paying member, it might also just be for consistency in how they handle the common free emotes and channel-specific emotes.
It takes a lot more effort, leading to some developer keeping his job. Also, it increases the maintenance cost, again leading to some developer keeping his job.