This is an interesting article on the topic: http://www.secretsofbabybehavior.com/2010/05/why-do-some-babies-hate-being-drowsy.html
The article has this to say on why some babies hate being drowsy:
-The Drowsy State:
Babies move in and out of 6 different "states" or moods: crying, irritable, quiet alert, drowsy, active sleep, and quiet sleep. You can tell what "state" a baby is in by the way she moves, breathes, and the noises she makes. I'm sure you all know that babies become drowsy when they are tired. Tiny babies tire very quickly, especially when they've had to deal with a lot of stimulation. Drowsy babies will stop paying attention to things around them, open and close their eyes, yawn, breathe faster then slower, and rub their faces with their hands. Some babies, especially younger babies, also get cranky, fussy, and increasingly frustrated.
-Why Some Drowsy Babies Get so Irritable
Babies are hardwired to learn and socialize with the adults who care for them. They stare at their parents' faces, watch their mouths, try to copy their movements, and often calm down when they hear mommy's or daddy's voice. As babies get older, they become fascinated by every new object they see and try to touch, taste, drop, and explore everything in their reach. Babies work hard as little scientists, experimenting day and night to determine cause and effect. They love to play repetitive games and will giggle with excitement when they "discover" how to make their daddies' tickle their tummies or to elicit their mommies' smiles. Anything that gets in the way of that work may irritate babies. Unfortunately, babies can't maintain that learning state forever. They'll start to get sleepy, even though their brains and bodies will push them to learn more and more. For some very social and determined babies, sleepiness is so annoying, they'll start to cry.
-Why Some Babies Fight Sleep
Some babies have a much harder time than others in changing their states, particularly calming themselves and getting to sleep. Fortunately, as babies get older, they get better at these important skills. However, all babies (even babies who regularly fall asleep easily), may struggle with sleep when they have been overstimulated or exposed to a stimulant like caffeine. Babies who are overstimulated (by vigorous play near nap or bed time, big changes in routine, or spending time in a crowd) have a hard time dealing with all the excitement. Their bodies react by releasing chemicals that stimulate their brains. Some babies will process these chemicals quickly, but others will not. Adults may have the same experience after watching a scary movie or attending a large party. In those circumstances, we can't fall asleep either. Some babies (and I had one) want the social time to last forever and fuss and cry and fight sleep with all their might."
A clear routine can help your baby settle down. It may take some time figuring out what works for you, every child is different after all.
From the same article
5 Quick Tips for Dealing with Babies Who Hate Being Drowsy
Prevent over stimulation or any prolonged stimulation, particularly at bed time and nap time.
Avoid exposing your baby to stimulants like caffeine.
To calm your drowsy baby, maintain social play but slow the pace, gradually narrowing the type and duration of stimulation your baby receives. Limit what your baby sees, hears, and touches. Try slowly narrowing your interaction to include only one sense. Let her look quietly at your face OR hear your voice as she nestles into your shoulder.
Start a bedtime routine with a slow steady reduction in stimulation. Many experts suggest 45 minutes may be needed for a baby who struggles with getting to sleep. Don't worry, this won't last forever!
Try sustained stimulation, like white noise and steady motion, to help soothe babies who are fighting their need to sleep."