As such, adding an extra scene so that we’d get background on Snoke before he was promptly killed off would be a waste of time.
While Snoke was a menacing villain that provided development for Kylo Ren’s character, he wasn’t not a focus of the film.
The Last Jedi is already the longest installment in the entire Star Wars franchise.
Rian Johnson previously cited the handling of Palpatine in the original trilogy as a reference; we knew nothing about the character until he was eventually expanded in the prequels.