Annual mixes are a way to brighten up public spaces or private gardens at relatively low cost. They are often referred to as wildflowers which is misleading as they often include non-native plants, such as orange Californian poppies, along with some native cornfield annuals such as blue cornflowers and red poppies, to give more variety. Cosmos is also often added to prolong the flowering period. Insects certainly make use of them.
If you wish to create a similar effect as the one in the picture you need to eliminate less desirable species such as thistles before sowing. To get a really good display in later years don’t rely on self-seeding but cultivate and sow afresh.