The permanent bonuses in both Alliance & Team servers cost 8 points for all types.

But in Express, it costs 16 points for Defense and 12 points for Expenses.

Any reasons why they can't cost 8 points same like Alliance & Team??

Permanent bonuses are not great in express, and afaik they want to keep it that way so they don't have trouble with the balancing of them. The temporary bonuses are quite well balanced.

Bonuses in general are the weakest on express if you think about it. 1980 turns and only 40 bonus points meaning if you will 20 turns or about 1.0% of total turns... compare it to tournament where you can get like 1.9k turns before bonus points but 240 bonus points and each 2 bonus points give 3 turns, ergo 360 turns. That would make turns from bonus points make up around 16% of your total turns.