Some veggies can be eaten raw without being cooked and they are tasty to eat raw. For ex, Though you can eat bitter guard raw, you don't, because it's that bitter. All veggies when eaten raw is definitely nutritious than when it is cooked. But not all you can eat so, you select which best suits for eating raw.
Secondly, some veggies when eaten raw only tastes at its best for ex., Lettuce. If you cook, not only its nutrition but also taste vanishes..!
To summarize, we eat some veggies raw because,
1. Veggies eaten raw are nutritious
2. Some Veggies don't taste good when cooked, also its nutrition value reduces
3. Some veggies are eaten raw just because it tastes good.