Unicode scissors emoji originate from two sources, and they both contribute to this plethora of non-closing scissors.
First, Unicode scissors character (U+2702) originates from ITC Zapf Dingbats series 100 [1]. As a result they have, unlike most Unicode characters, pretty much standardized reference glyphs. And scissors glyphs do not completely close too there.
Second, the original emojis were implemented in limited space (say, 16 by 16 pixels) and the design was constrained. In some platforms (especially SoftBank) they were animated instead, and indeed there were some reference emojis that close only in the animation [2].
First, Unicode scissors character (U+2702) originates from ITC Zapf Dingbats series 100 [1]. As a result they have, unlike most Unicode characters, pretty much standardized reference glyphs. And scissors glyphs do not completely close too there.
Second, the original emojis were implemented in limited space (say, 16 by 16 pixels) and the design was constrained. In some platforms (especially SoftBank) they were animated instead, and indeed there were some reference emojis that close only in the animation [2].
[1] https://en.wikipedia.org/wiki/Zapf_Dingbats
[2] https://unicode.org/emoji/charts/full-emoji-list.html#2702