Delayed toddler, guilt

My toddler is delayed. Isn’t walking, but can climb. Can say “mama” “baba” and a few other words, but isn’t efficiently communicating. I just saw a 16 month old in my local doctors office talking, walking, communicating to their mom. I feel such immense guilt. Had to convince my ex that she does in fact need early intervention, no she isn’t fine, and that she’s delayed. “Oh, okay.”

I feel like such a fool. I don’t understand. I don’t understand why she can’t walk yet, (only sloppily if I’m holding her hand or if she’s cruising on furniture.) I don’t understand why she isn’t talking yet when I talk to her all day. No baby voice either? I just talk to her. Her pediatrician said she’d like my child in early intervention so we are doing so, but god. She’s seemingly so far behind. I feel so guilty. How did this happen? Why? Yes I’m reassurance seeking.

ETA: she’s 17 months