Where did the L in talk go?

In standard pronunciation the l is silent in "talk/walk" and similar words (see list above). This is a matter of simplification of pronunciation. After the long vowel /o:/ (this is not the correct phonetic sign) the consonant group lk is regularly simplified to /k/ as the clear pronunciation of /l+k/ would be cumbersome.

I pronounce the L in talk, walk, chalk, and other similarly spelt words. I believe it's a subtlety that is lost with familiarity. In fast speech, the pronunciation of the L is indistinguishable from saying the word without the L. This is why I believe most people believe that the L is silent. In slow speech, the L is noticeable.

I've noticed in Southern United States accents where the pace of the speech is slower and the contraction "y'all" is used a lot, you'll hear the L.

The people that I've met that pronounce the L like I do interestingly have something else in common with me, they have tried to shed their regional accent. I think people who become very conscious of how they enunciate words tend to work harder at the subtleties of pronunciation. Those that don't just settle for or acquire the regional accent.