Why does sperm produce in lower …

There is a thing called 'maturing'. Sperms are not produced at the time of ejaculation. Actually it will be produced for days. After that they will mature gradually. This maturing process needs a very careful handling. This needs many essential things like vitamins,hormones,proper temperature range,etc. Within the body, temperature controlling is not advisable, because some organs need heat for their proper functioning. Especially for a male many of his organs work good in elevated temperatures. So, the body is having a convenient place to grow the sperms thereby the outside, where it can keep the required temperature without affecting the major organs.

Heat is a factor that can cause great damage to DNA. In the testes where spermatogenesis (sperm meiosis) occurs you definitely do not want DNA damage occurring during or after this process as it could have devestating effects for the offspring. Hence, in a warm blooded human the testes are dropped from the body.