The main issue with this is that certain regions can shrink over time, even to the point of non existence. You can argue that it might just be a 'skill issue' but the reality is if VCT wants to succeed it needs to draw in viewership from across the globe, and making it so regions that aren't as competitive don't have a chance to develop in tier 1 really limits that.
Plus that's not even part of the financial argument, what makes VCT tier 1 so attractive is that it's one of the few esports leagues which may actually be able to turn a profit, and the only way to do that is through long term stability. I agree that tier 2 doesn't make sense right now but relegation would make tier 1 not make sense in the way it's been envisioned. It took football 100's of years to add relegation. I don't think it'll be a wise move until maybe like 10 years down the line or so before relegation can be seen as a viable option for VCT, it's simply too small for now