A dog's nose gathers details like identity, gender, mood from genital smells. It's like reading an ID card.
Sniffing genitals is ingrained social behavior for dogs to gather information. They don't understand it's rude.
Intriguing new smells attract dogs. Repeated crotch sniffing becomes a habit.
Interest & Habit
With positive reinforcement, train your dog a solid "leave it" cue to discourage inappropriate sniffing.
When dog goes for a sniff, redirect focus to another behavior like a trick or obedience command.
Keep dog leashed, use baby gates - limit access to restrict opportunities to sniff private areas.
With patience, gently teach your dog groin sniffing is unwanted by praising non-sniffing