The problem, GG2, is that you don't understand how those scores are actually being achieved.
You play complete rounds. Most of those "low score" players do not. Sure, it's possible for lightning to strike and get a low score on the first attempt but it doesn't happen often. Most of those players set a score goal for each hole. They start the round all over again if they fail to hit that target on a hole. They might start a tournament round hundreds of times before they actually complete a round and post a score.
Add to that the fact that many players in the higher tiers have thousands and thousands of complete rounds under their belts. They have a tremendous amount of time, effort and credits invested in this game. They've taken the time to optimize their computers. They have notebooks stuffed with information. They've learned the nuances of the game and the courses. They have a knowledge based on extensive experience far beyond the rest of us. Many are also simply better than we are at playing the game. They are able to post low scores consistently as a result of all that.
Is there cheating here? Of course. Many of the absurdly low scores being posted at lower tiers are actually upper tier players who have created multiple accounts to take advantage. For the most part WGT won't do much about them because it pads the number of active accounts that WGT can claim as active users to advertisers.
Most of the upper tier scores are legitimate, though.
The best thing you can do is play rounds with friends, treat this as entertainment and not fret about being competitive in any WGT sponsored tournaments. Find an honest country club and play those tournaments.
Only play WGT tournaments when they are free and on courses that normally have green fees. That way you save a few credits and get to play those courses for free. Just don't set any competitive expectations in those tourneys..