You might find it curious by what happens when your signing baby starts to talk. They’ll pick and choose which words they say and which they sign. For example, my signing baby signs and said MORE, DAD, BIRD and several others, but would say “banana” just as soon as he could. I guess he just found the sign too cumbersome and the word easier to say.
That’s the beauty of teaching signs though because there will be some sounds that your baby will find difficult to say out loud. So instead of handcuffing your baby like non-signers, your baby will have options. This notably expands their vocabulary and gives them a more complete mastery of their environment.
When most words are easier to say than sign, then signs will get dropped. It’s not that your baby doesn’t like to sign or wont so long as you do, it’s just that saying words is so much quicker and easier for hearing babies. By nature, we’re a pretty lazy species, so if and we shortcuts present themselves, we inevitably take advantage.
Instead of holding your little guy back, encourage them to speak up and exercise their voice just as you did as they learned to sign. Signing was never meant to replace talking, it was merely a stage to work through.