Just to add to Dreamboat, afaik the reason relays have stopped being used over recent years is due to some unknown bugs causing mad lag spikes inside the STV relay making it unviewable. Here's an example from a past ESEA cast.
https://youtu.be/I2AihrVthrI?t=1491
ESEA, ozfortress and serveme EU all used relays and which gives context as to why ESEA STV's sucked a lot. I don't know if someone had a solution for it but if anyone does please reach out!
on the note of mustard's screenshot, please note I don't support RGL's decision and was only offering some insight on why they probably had these rules.