It's standard practice in sports sponsorship to have "sector exclusivity", on the basis that branding partners are paying a premium. A long time ago I worked with a sports marketing agency in Asia (essentially run by a football agent) and they were hawking shirt sponsorship deals around for 2 Prem clubs. (This was around the time Emirates were taking stadium naming rights for Arsenal - I can't recall if they were the first or Reebok at Notlob were).
You would have a standard kit of parts which is what benefits they would get, and there was negotiation / flexibility around that. Some companies wanted to involve their "customers", so wanted to package competitions to win a corporate box for a day at X, etc. It really depended on the sponsor's business model.
Around this ecosystem there was a compay that used to measure sponsorship exposure. So each match would generate a ROMI (return on marketing investment) report that would provide metrics related to brand exposure, and convert to dollar value. Remember, at the time the number of games broadcast in UK was a lot less, but overseas was more, and moving towards all 380 games (which happened in the late noughties).
I saw the sponsor list that Man U had. And it was like a Yellow Pages directory of every sort of company and a lot of them nothing to do with the UK. They had an official Clock Partner - a Japanese company. I suspect they didn't pay much, but it gave them the rights to associate their brand with Man U in their markets.
The point I'm trying to make
@davek is that 20 years ago clubs were way ahead of us commercially. At one stage in the early noughties our neighbours commercial revenue alone (i.e. sponsorship) was more than our total revenue (matchday, commercial and broadcast). Think about that. Meanwhile if we're paying Grealish full wages, then my Forever Blue+ membership (for the opportunitiy to bid on a ticket on one of my 2 trips to UK this season) will cover 2 minutes of his wages.
I know you have a hatred of our sponsor, but I've seen messages (that I actually have permission to share and have done with some) that say to me that we may have actuallybeen rather clever, and found a sponsor that is keen to develop with the club, and thinks it will bring revenue opportunities to them.
(And for the record, I agree with the sentiment that the HD branding is a bit OTT).