Is there any lore as to why this is? It just baffles me.

I'm not sure if there's any lore behind it, so just my thoughts. Once you contract vampirism you have to go to sleep, or wait i think, for much to happen. So for example if you're at 25% vampire for the first day (if we assume you go to sleep once a night) and grow by 25% each time you rest until you're at 100% obviously, you're going to become more hungry to feed, its agitating you, filling you with the hunger, making you stronger. The only thing to quench your thirst is your next feed, the longer you go without the harder it is to deal with, hence the sunlight damage, i will assume that the gained abilities offset the sunlight damage and vice versa. That seemed to make sense in my head as i was typing it but as i read it back to myself it seems to only further your question =/ Lets hope for the both of us someone actually knows the answer...

I totally understand what you're saying Deryck! in the vanilla game, there is no real incentive to be a vampire. Luckily, there are mods out there that actually do make you realize that being a vampire can be a gift, not a curse.

@A-2TheK: The way I see it, There are pros and cons of not feeding. I guess Bethesda thought that feeding for being able to walk around in sunlight is a better pro than having boosted stats.