It’s not about having “the best” refs, it’s about protectionism and being in control of the refs

Overseas fan here so i’m not that familiar with the refereeing appointment system in English sport. Just watched some UCL highlight and notice in some matches, all 4 referees are from different nationality. Referring the the Premier League after all the scandalous events happening with VAR recently, I’ve come to the above question: Why are Premier League’s referees all from UK?

From the look of it: Premier League has the best players in the world and the best managers that money can buy, heck, even non-sport related managerial positions of top clubs are filled with seasonal international executive. Yet, every appointment of referee in every premier league game are all from England (or UK?). Why? It’s not like they can’t afford to pay top referee in the football world right? So what stops PGMOL from hiring and appointing top ref regardless of nationality to Premier League matches? Football referee protectionism?

And if PGMOL change and start appointing international ref, would you think the ref quality will improve vs status quo?

Btw, this is not to say English ref are not good. The simple truth is limiting your resource pool to just nationality will obviously affect your output quality.