Pace of play is a threefold problem: 1)The course itself 2)Slow players 3) USGA rules don't make play fast.
First of all imagine a course that is old with greens that are small and curvey, bunkers around them with different types of sand, some with not enough sand, greens that roll at three different speeds and change daily, uneven watering, 16 holes that you can bounce off the green into OB or 8inch high grass. Blind shots on fairways that bounce toward hazards with tall grass. Sure you can play it in 3.5 hours and I have walking it, but it ain't going to happen when you start putting just a few foursomes in front of you, especially when a public course can't resist the temptation to pile them on as fast as they can.
Next slow players, these idiots have no concept of time or what they should be doing to speed up. My belief is a Marshall should stand over the group and say stuff. Like it's your turn do it and why didn't you check out the putt instead of standing around waiting and so on.
USGA rules don't encourage fast play, you want add two strokes to your score or would you rather have a chance of making par, that means you need to find your ball! More than half of golfers don't go back to the tee for a white OB stake, so make it one stroke and call it a hazard, too many courses use white stakes to try and control speed of play, but it doesn't work.
So it isn't just the golfers it's the whole system.