Not least because the publications offering fledgling writers exposure in lieu of payment generally aren’t read by anyone with the power or inclination to hire you.
What can work is writing to build your portfolio. Take the unpaid gigs when you need to, but make sure you knock the work out of the park.
Then, when you’re applying/pitching for paid work, show them those assignments to prove to them that if they do hire you, you’ll do the same for them.
Writing for love also works: because you love what the publisher stands for, you want to create something awesome with your friends, or you want to do a friend a favour.
But the publishers that offer writers genuinely good exposure? Are almost always publications that pay their writers a respectable wage. Or something approaching it, if they’re small and indie.