The translation “表情” is less accurate than “贴纸/贴图/图贴”. “表情” should refer to Emoticon or Emoji.

nope, In China, "Sticker" is used as "表情" more wildly.
BTW, Sticker itself is expressing the meme, emoticon, emotion-related or any other things. Line is a good example. Anything like logo seldom appeared in Sticker.
In addition, Chinese uses "表情" more than its original meanings. Memes can be used as "表情" also. You can't say it is less accurate than other suggestions.
Even more, whatever "表情" or "贴纸", people can upload anything as one of them at any time as they wish. Even pornography is allowed.

An example in other string: Saved Message in Russia is translated as "Favourites".
Their meanings are definitely not the same. You can say favorites can only be used in Browser, or why Telegram won't use it instead of "Saved Message", Telegram can upload up to 2.5GB ,etc.
In fact, it is just because this is wildly used and natural. If you talking about its accuracy, of course, it is not.