That's because there is not one single way to draw crowds back to 25-man raiding that doesn't either come off as emotional blackmail (Look what you can't have 10-mans!) or making 10-man players feel like second class citizens.
At the end of the day, you can take out all arguments about logistics. You can also remove those people who prefer 25s but are doing 10-mans due to an inability to find a raid. You can distill it down very unemotionally to a couple of points:
- About 15-18 people in a 25 man raid didn't enjoy or embrace the larger raid size on the merits of it being 25 people. They sacrificed convenience, put up with longer wait times between pulls and became a faceless cog in the machine purely for the better gear.
- When the gear item levels became the same, Occam's Razor dictates that most of those players took the path to 10-mans because they saw zero value in wasting the time with 25-mans. Path of least resistance. Less annoyance, less time wasting, more fun. Same gear.
- If the only thing keeping 25-mans popular was the gear, and they functionally offer nothing else better for the rank and file members of a raid, then darwinism dictates they should either die or be solely supported by the players that want to raid 25-mans.
- I say this as a random 10-man player addressing a 25-man player: This is your problem. Not mine. Fix it yourself without ruining my fun.
Any way you look at it, "incentives" for 25 man raiding are all about emotionally blackmailing people who'd rather be doing something else into subsidizing the fun of 25 man raiders... At the cost of their own time and fun.