"Hospital Gift" vs. Original Birth Certificate?

I tried to get my drivers license today (Texas), and was denied because my birth certificate is not a legal document. That didn't make sense to me because it had the seal on it (Colorado), and I've used it my whole 18 years of life. It got me through school, it got me a job with the state of Texas. So why isn't it good enough for the DPS? It's what the hospital gave my parents and it's what we've used my entire life. I had to order an original from the county I was born in, and man was that a hassle. So I'm just wondering, what's the difference? Also why didn't the hospital give my parents the original, "real" thing when I was born? Or does everyone have to obtain that later?