"If taste buds are on the tongue, why can’t I taste food until I chew/bite it?"
You only have 5 senses on the tongue, these being: Bitter, Sweet, Sour, Salt and Umami (which is a savoury/meaty taste, normally attributed to mushroom/earthy tastes). There is research into another sense on the tongue, this being fat, however this is in the early stages.
All other taste senses come from your nose. Therefore you can’t really taste anything, not strongly anyway, until you close your mouth and the chemicals from the food can find their way to the receptors on your tongue and also in the nose.