I guess because they want you to play? It sounds like if a game uses this trinity thing you hate so much you won't even consider it. If there are enough people who feel the way you do, I guess they want to get your attention.
Personally, I think if a game is good and fun then it shouldn't matter. But I'm more interested in just playing the game and the story than in figuring out all the intricacies out of system. As long as I am enjoying myself, then I'm satisfied.
I know you hate it. Trinity bad, force multipliers good, got it! You hate it so much and the players who use it that you designed an AE arc specifically to punish players who play that way. Lighten up.
More like dynamic gameplay good, the same thing "over and over and over and over and over and over and over and over again (add infinite) bad. I don't play games where I find myself exclusively using only one tactic. Stop having fun guys may love forcing others to only use one tactic, I don't(I'd rather force people away from one tactic so they have to use and experiment with dozens of others and discover there is so much more out there than one very, very old tactic).
Besides good gameplay, the good game in a way leads you to do more then just resorting to the same tactic every time without making you dig deeper into raw stats all the time.
For me, fun has to avoid the same all the time. There is a saying, "To much of a good thing kills it".
As for me AE arch, it's also cause I think the trinity is unrealistic. Not being the stop having fun guy, more being the one saying it's time to try new things for once. Non trinity play is also especially fun done right, 100s of times more so. My arch was made for advanced players only, with teams who were at the top. There were more then one way to fight the mobs I made, just they were made so initiative and good reactiveness mattered, not constant deliberate planning around bad AI. Lua scripting would have allowed me to really create the grey area I wanted to achieve, to.
I remember, Matt Miller even said, that the holy trinity is more like a puzzle game. People who like the trinity, like puzzle games, because they can be taken down all the time repeatedly every time with the same solution every time with ease. So a holy trinity encounter to me isn't even a fight, it's a puzzle. And the thing is, puzzles, once you solve them once, doing the exact same one again isn't the same as the first time, it gives not the same feel. I'd actually like pvp if it was better in mmorpgs, but it never is. I used to pvp all the time in CO until it got boring(And people began using the same tactics over and over again, ugh I remember the uppercut spam days, those lead me to stop, and I was usually stomping uppercut spammers with ease).