I strongly suspect age discrimination comes into play, either consciously or unconsciously. In some cases, the team lead making hiring decisions is young enough

I strongly suspect age discrimination comes into play, either consciously or unconsciously. In some cases, the team lead making hiring decisions is young enough to be my son, and experience on my resume goes back to around his birthdate. Putting myself into the young team lead's shoes, I think he isn't comfortable hiring the older, wiser developer, however stellar the resume -- he probably wants a team of hip, young 20 and 30-somethings, and if they come cheaper, so much the better. So he doesn't even bother to respond. It's not hard to extrapolate to a time when all the people making the developer hiring decisions think like this, and you see the writing on the wall, and try something else.