The problem is that Netflix has its own Stranger Things experiences right now. They started in 2020 and will probably keep going for a few more years.
I've heard that Netflix gets very greedy when it comes to merch, wanting a pretty good percentage of the profits made from merch at HHN. With them running their own experiences, they get every penny spent by guests. It's just not smart from a business standpoint for Netflix to share it's IP right now.