But Bosman wasn't until 95.Everyone loosened domestic players quotas because of the Bosman ruling that allowed free movement for EU players within EU. And while the first division wasn't as popular as it is today, when I was growing up it Greece in the 80s and we had two tv stations, the only match I could watch live on the whole weekend was an English first division game on Saturday afternoon; not even Greek league games were shown live back then. Then you would get highlights from foreign leagues on sunday nights and the English first division was the first.
Oh and btw, the English division had an advantage over others, because the average European team could only have two foreigners, while English sides could have Welsh, Scots etc. They may have been able to sign commonwealth players too; I am not sure for example whether Bruce Gropelaar who was South African players a foreigner or a domestic player with Liverpool.
What happened IMO is that the EPL was a rebrand that was accompanied with stadium upgrades, an infusion of new TV money and free player movement (like everywhere). the difference was that the English league was the most popular abroad to begin with so it was always the first league to sell their TV rights abroad, so they got the best deals, which led to better players, which in turn improved to more people abroad following it, more merchandizing being sold, more money into the game, better players being signed, which in turn led to better TV deals and so on.
Basically a small initial advantage snowballed into a larger advantage over the rest of the world.
And maybe you're right that the EPL was more popular as a league, but growing up in the 90s the Italian league was considered by far the best, and the best clubs were considered to be Milan, Juve, Barca, Madrid, Ajax (it really doesn't get better than mid 90s Ajax for nostalgia), and United.
Looking back to 90s TM data, EPL clubs started spending alongside Italian clubs (+ Bayern, Barca, Madrid, etc.) around the time of the EPL founding, were firmly in the mix of biggest spenders by 94-95, but surprisingly EPL clubs didn't dominate the transfer market until much later. Someone more astute than me can probably explain some of this with financial mischief (looking at you Serie A). But the EPL started to ramp up transfer spending again in 03-04 (e.g., Crespo, Makalele, Mutu, CR7, Geremi, etc.), and by 06-07 you had clubs like Spurs and WHU matching the biggest international transfer fees of Inter, Barca, etc. By 07-08, the clubs associated with the biggest international transfers looks remarkably similar to today with some funny outliers (e.g., Valencia, Middlebrough, and Lyon spending big).