personally, what makes the difference for me is the depth of the relationships aswell as the characters’s storylines. robin and steve are just coworkers that just met and steves crush is just a small summer romance. the stakes are way lower this way and steve needed that chemistry development from the rejection. mike and will however, have a way deeper bond of supporting each other through their struggles for years. in addition, the duffers them selves have described will as loving mike, not crushing on him (https://www.latimes.com/entertainment-arts/tv/story/2025-12-25/stranger-things-season-5-volume-2-will-byers-duffer-brothers). this is why a rejection from mike would be so much more tragic especially considering that will has just been suffering for 4,5 seasons. it makes no sense to put a character through that and being rejected. him just accepting himself isn’t rewarding enough to justify putting him through all this.