Plurality of "genitals"

Solution 1:

In English, certain nouns are usually only found in the plural form. They tend to be items which are found in/represent a pair, set, collection, etc. For example:

• Scissors
• Pants
• Tweezers
• News

Genitals falls into this category as it represents, as phoog pointed out, the reproductive organs collectively. Referring to my genital, or saying I have a genital would be very unusual.

Solution 2:

It’s because it’s a translation of the Latin plural ‘genitalia’.

Solution 3:

I too find it a bit odd, but I think the history behind it is that "genitals" actually refers to the several reproductive organs collectively.