Nighties for men do exist. In English speaking countries, they're referred to as night shirts for men and you will find night shirts in a variety of fabrics like cotton, jersey and stretch in short, mid or full length models.
We are more inclined to recognize however that there are men who are really looking for nighties; let's say in the feminine sense. A soft, comfortable robe which hugs and compliments the body with light subtle designs or even just in plain pastel colors with matching briefs and slippers. Why not add a warm, soft and cozy light weight fleece gown for those cold wintry nights in front of the tele?
In reality, the perfect nighty for men can be found in boutiques which specialize in nightwear for women.