Vocalizing depending upon muscle strength in the mouth and has nothing to do with you saying mama, dada to the infant. I don't know why more people don't know this.

The act of suckling strengthens lips, tongue which are what we use to vocalize. It turns out the easiest sound to make is 'ta', it only needs a little bit of tongue to do. The next sound is 'da' which requires a little more tongue work, but not much which is why statistically the first word out of a babies mouth is dada, it is easier to say. Making the sound 'ma' require lip strength. Lips muscles are hugely weaker than tongue muscles so 'ma' and 'ba' and 'pa' take longer to master for the baby.

Babies speak as per their physically development not so much what you train them to do.