All versions of the game are faster and looser due to the switch to Simonis 860 cloth. Similarly, the nappy cloth, composition balls, and less lively rails of yesteryear required a somewhat different, and more patient, approach.
I may be a little off on the dates - grew up without a TV and never owned one - but have always had the notion that TV was the original driver that sped the games up including the equipment to keep up. There was a period from the late 60's through the early 80's when there was a lot of pool on TV and tournaments paid pretty well (constant dollars, compared to today).
In return, "fast" moving games and rules made it more interesting for the audience, and fast games with simple rules were promoted (Tex express 9 ball). Slower games died - how friendly is 14.1 for TV audiences who don't know much about pool at all? It may have suspense for those in the know, but (on the surface) it lacks the steady, quick, confrontational aspects of other games.
Before that TV era, the rules were more variable and even "complicated" to give a range of gambling options as others have mentioned above. Always possible to negotiate a rule system to make or break a perceived advantage or enhance the payoff before coming to terms for the game. After TV, they were adopted to create a type of interest that would hold non-traditional viewers bred on kinetic & hyper-kinetic sports, and attract sponsors.
OTOH, Snooker has a huge viewership in some countries and is "complicated" compared to most pool games, so things could swing the other way if there was anyway to increase the fan base.
smt