Why are some very prominent apps/services like Google Maps free?

Answer 1

As you have heard, "There are no free lunched."

Many, many information services have adopted a model of (1) contributions from appreciative consumers [see the yearly Wikipedia request for support] or (2) advertisers pay to have their ads included at various spots on the pages produced [e.g., YouTube, Google, etc.]. The former marketing strategy is used by PBS (no commercial ads to interrupt programs); the latter is like the Super Bowl [here, some say the ads are as interesting as the game].

A few efforts (e.g., Khan Academy) have industry partners (Khan Academy gets millions from Microsoft because world education is a priority].