The reason doubtlessly varies greatly from person to person. I'm currently maxed except for lavas (half way) and heros (18/17) with no plans to go to TH10 until I'm done with walls. Here's my main justification, if your goal is to have lavas at TH10 or even zap the fastest possible method to achieve this is to grind them at th9 even with sleeping builders.
We debate a number of items on these forums, but one item that nobody ever calls into question is the fact that loot is significantly better at TH9 than TH10. Lets continue with that assumption.
For player 1 lets say they take 3 months with all builders asleep (unrealistic since you'd probably have atleast heros) to grind out lavas at th9, player 2 goes to TH10 with Legos or worse. For the sake of simplification lets assume both take exactly 9 months to max all building at TH10.
z=sleeping builder
a=active building
|
Month1 |
Month2 |
Month3 |
Month4 |
Month5 |
Month6 |
Month7 |
Month8 |
Month9 |
Month10 |
Month11 |
Month12 |
| Player 1 (Max TH9( |
Z(grinding walls) |
Z(grinding walls) |
Z (grindingwalls) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
| Player 2 (early TH10) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
a(upgrading TH10 defense) |
Z(grinding walls) |
Z(grinding walls) |
Z(grinding walls) |
As you can see, at some point both players will be grinding walls in order to reach their goal of TH10 with lavas+ with sleeping builders. The difference is that player 1 who maxed TH9 will achieve this much quicker as they did their massive resource grind at the more lucrative TH9 instead of TH10. This may not be the "fun" way to play for some people but it will doubtlessly be the more productive.
As for those who believe you can "hold onto" loot better as a TH10 that argument has zero merit. I haven't lost more onegold storage to an attack in 8 months since nobody uses strong armies in the gold farming range against near maxed TH9s.
I understand plenty of people will disagree with this play-style, I'm just explaining my decision for you benefit since that was the original point of this thread.