It's pretty simple.
The current raid design annoys (maybe) 10% of the 5% of the player base who cleared the former raids.
While doubling or trippling the overall clears at least.
It's much better to enable 10.000 people raiding 4h a week and clear all in 3 month, instead of focussing on not losing those 100 who clear it in 2 weeks.
Even if they need 6 or 8 weeks... that's 100 ppl subbing a bit longer and 10.000 who cannot attemp it at all again, because of time/skill/static needed.
