The birds are back! (Coal Tit, Robin, Sparrow, Greenfinch, Wren, Blackbirds)

I have had bird feeders filled with seeds, peanuts and mealworms through winter but the feeders have remained unused and the birds nowhere to be seen. Now the sun is starting to warm the days (in between showers and hail), a small cloud of Coal Tits, a Robin, a few Sparrows, Greenfinch, a Wren and a couple (M & F) of Blackbirds all visited my garden this morning. My question is - why did the birds not feed over winter when the food was so freely available? What could I have done and where have they all been hiding until now?