It is hard to tell exactly why your local bird population may have dispersed, but here are some possible reasons:
1) Something may be wrong with your bird feeder station (if you have one).
Seed gets old, and can go bad. Also corn can get moldy very fast. Depending on what type of bird food you may have in your feeders it may be time to replace it. In addition you could have a disease issue if feeders are not regularly cleaned. In addition if you have made any major landscape changes in your yard this could effect the birds ability to feel comfortable. More great info on how to create a safe feeding environment here: https://feederwatch.org/learn/feeding-birds/#safe-feeding-environment
2) A new predator could be in your area. Natural predators like Cooper's Hawks or Merlin can sometimes set up residence near your yard which could deter songbirds. You can try to plant cover like juniper bushes, cedar trees or other native evergreens to help provide a safer hiding place for the song birds. In addition domestic cats can be a huge problem for wild birds. It is estimated domestic cats kill approximately 2.4 billion birds every year in the US alone. If you have your own cat it is best to keep them inside (they live healthier and longer lives that way too). Encourage neighbors to do the same.
3) Natural food sources may have shifted. If a natural food source is particularly abundant in a nearby area, or a local natural food source from your yard is absent this year, then that can shift where songbirds congregate.
4) Migration can mean your local birds are headed somewhere else for now. Many birds have annual regular cycles of migration like Orioles and Hummingbirds. These species depart and return on regular cycles and will often return to the same area. However, other birds like Blue Jays, Chickadees, and Finches have very irregular migrations. In some years they won't migrate at all, and in other years they may migrate East/West or North/South depending on weather conditions, food availability and a variety of other factors. You local birds could be in some form of migration right now. Robins are great examples of irregular migrants, and they are certainly migrating now, so your local winter population may have moved farther north as the weather breaks up there.
5) There are major shifts and declines in many birds species across the world.
Sadly things like domestic cats, habitat loss, window collisions, light pollution, over use of pesticides and a variety of other factors have caused huge declines in bird populations over the last few decades. Although this is probably not what's been effecting your local bird population in your back yard on this short term time frame, it is a larger problem that can be causing shifts to your backyard bird populations over several years. To learn more about the problem, and what you can do, check out this link: https://www.birds.cornell.edu/home/bring-birds-back/
Hope that helps, and let me know if you have more questions :)