How did photographers share and get feedback on their work before the internet?

People who were new to photography showcased what they did on a much smaller and local scale, often limited to friends an colleagues. But a number of magazines, newspapers, and other groups did run photo contests, often with prizes for best photos. Many were national and many were local. Some cities have local photo clubs. Some community galleries would host photos of local photographers. In my own area we have Artworks around town, inc that has a permanent gallery where local artists, including photographers, can display their works. Similar venues exist in many other communities. Check your local newspaper.

On the internet, it's not just places like Facebook. Even here in stackexchange phography section, there is a Weekly Featured Image you can see at the top of the pages here. Google's Panoramio site also has a photo contest each month for featured images in Community >> photo contest. There are number of photography specific forums around, too.