Because they sure don't look like birds to me.
4 seconds sound clip from the Jurassic Park (1993) movie soundboard.
You can hear this line at 00:39:35 in the Blu-ray version of the movie.
Quote context
[...]
- Dr. Grant, come in the second car.
- I'm gonna ride with Dr. Sattler.
- I read your book. That's great.
- Do you really think dinosaurs turned into birds and that's where they went?
- A few species may have evolved along those lines.
- Because they sure don't look like birds to me.
- Listen... Tim. Tim, which car were you planning on?
- Then I heard about this thing in Omni about this meteor making all this heat.
- And it made a bunch of diamond dust and that changed the weather.
- They died because of the weather.
[...]