It's that bad it does almost seem like a conspiracy at times, but to be honest, I just think they have a freaking tough job with extremely hard guidelines to follow and lack of accountability for poor performances.
I shall elaborate.
The job itself. Everyone will tell you how much the game has changed in the past 20, much quicker, way more players at each contest, faster skills, players trying to use certain rules to their advantage. All of these changes, plus rules that now contain more interpretation rather than black and white scenarios.
With all of the above its just a really tough job to get consistent calls. I myself think I am a reasonable judge of frees and unbiased, yet I can be watching on the best angle available on TV and go completely apeshit bananas when a free isn't paid, just to see the replay and realise I was wrong.
Umpires are just human, they have the pressure of on the spot calls, pressure from the crowd and all of the above factors in a fast paced game, it's a seriously tough job.
Lack of accountability. It irks me that week in and week out there is (or used to be) a segment with the umpires boss assessing some of the dodgy frees from each weeks games. It was total BS as they manipulated the interpretation of each rule to get the outcome of "the right decision was made" - unless it was an absolute shocker.
To me this is ridiculous, the umpires always seem to have been untouchable, coaches are even too scared to comment. I really hope that behind closed doors they are getting the honest feedback that they deserve.
Fixes. It has to come down to simplified interpretations. Especially HTB as it is just impossible in the speed of the game to decide if a ball was knocked out in the tackle etc etc.
Better internal feedback and accountability
Another thing I would love to see is players being paid a free kick against if they appeal for a free kick, nothing annoys me more these days than 5 players staring at the ball as it rolls over the line then all turning to the umpire and appealing for a free, or 5 ppl sitting on top of each other then all appealing for HTB.
Start paying frees for this pathetic behaviour and that's one less thing the umps have to be influenced by.
Can't say the above ideas will fix it, but I also can't see how they could hurt.
Plus - I think there is a clear difference in wet games, seems to always be less frees paid, might just be my imagination.