You bring new trials in so you can see how they perform and if they overall fit into the team. This does not mean you expect them to push out the most numbers disregarding everything else. Are they doing mechanics? Do they follow raid callouts? Are they willing to risk wiping the raid just to look better on logs?
It makes logical sense that you do not prioritize trials over those who are already established raiders you know you can rely on. This does not mean that trials do not get loot however, and the point of farm is to bring in trials, and give loot to them unless it is a major upgrade for a raider.
Keep in mind that this is being done because the loot you get from bosses belongs to the group. You are someone who just entered the group, working on becoming part of the group. There are so many guild hoppers and loot-centric players around that if you do not take pre-cautions they can just end up walking out of your guild after taking away 4-5 pieces of loot after a two week period.
Guilds distribute loot so their raiders, collectively and, hopefully evenly, so they can more easily tackle bosses that are not on farm. A non-RNG based loot system can of course help on this issue, and it may be time for Blizzard to consider options in that direction instead.
In guilds who used master loot now the difference is that they use RC loot now to distribute the loot, and that during the first few weeks of clearing it isn’t used because there isn’t really anything that is tradable. After that sensible guilds go for the even distribution method, where they try to aim to maximize the worth of the piece of loot.
PL is against that, but I feel it isn’t really working either. It was designed for pugs primarily (hence why at the start there was an option to use ML still if 80% of the group was guildies) but with the scarce amount of loot available from raids chances are you will barely, if ever see any loot at all. Roll tokens were meant to help out with this, but for some reason they dropped the idea.
I think the biggest issue raiding faces now is the fact that the newer generation that decides to jump into the game now are loot oriented, since that is what Blizzard advocates with its current seasonal game design. Raiding as a concept is about overcoming obstacles as a group, which goes directly against the notion that loot belongs to an individual. It belongs to the group, collectively. This is a way of thinking Blizzard needs to change, or they need to change how raids operate, because currently the two aren’t blending in really well.
We also have a new type of player joining into this mixture, which are M+ players. Most of them do not care about raiding, and just want the loot so they can push as high on the M+ ladder as possible. It is a bit hard to distribute loot in this case, since it is almost guaranteed that as soon as these players get the loot they want they stop showing up to raids, dropping your raid roster by one. You have to start looking for a new recruit once again, who again can easily turn out to be another player who is only interested in M+.