Sponsorship revenue always gone up. It has been steadily going up from the day they took over United.100%. Sponsors are there because the fans are there. This is the basic fundamental idea of every sponsorship. You take the fans away or get the fans to actively turn against the sponsor (Same effect), the sponsorship becomes worthless to the outside company and they either do 1 of two things. 1) pull out immediately as they gain no benefit or actively get their brand image harmed or 2) Renegotiate for future deals and say something along the lines of 'we will not be renewing the contract once this current one is up'
If you believe you cant effect anything then you aren't really thinking at the scale of things required to cause this. Just remember this parasite cnuts get the balance sheet given to them every quarter. They only care about the number at the bottom. If that number starts dwindling that's when they will start thinking about how its becoming a losing business for them and jump ship. This was always the only way this was going to end. They were never going to sell by building up a brand. They would only sell after its become obvious that it had become a losing business.
So whatever strange concept of "hit them where it hurts" is a fairy tale, so far nothing happens, and United remains one of the biggest brand in football. We were awe strucked when Nike signs a 75m sponsorship deals with us which is pretty big back then, peanuts these days. Team Viewer alone pays us much much more for using their brand on our shirt.
So... good luck with that.