Loki is arguably the franchise’s most beloved villain, so for Thanos to kill him and take him off of the board (particularly after his heroic turn in Thor: Ragnarok) could easily help The Mad Titan become the big bad that Phase 3 deserves.
There’s a tremendous amount of anticipation for his character to finally do something big in the MCU, and many people involved with Infinity War seem to recognize that.
Some have voiced concern over whether or not this scene will potentially lead to the death of The Trickster God, and it makes sense from a thematic point of view.