It's expensive only if u don't  believe Chinese ones and want to buy branded.... Otherwise very cheap ones are also available I think

Because cost is inversely proportional to size!

That can be the only explanation.

ask the condom companies.......or convince your GF to stop using condoms with her

Supply and demand economics.  Too many people buying them.

But the larger sized ones are cheaper....less demand don't ya know.

Also quite a good reason to explain the population number

Personal experience. Chinese made condoms might work. Western made condoms work. What value can you put on your and your partner's safety?

not as expensive as catching a disase or having a child

Compared to the price of booze, condoms are not expnssive at all.

Compared to what Bat22 says above, condoms are MEGA CHEAP!!!!

Because there is always a large demand , including needs from the guys above.