The reason is that here in the British Isles we still celebrate the ancient Christian festival of Mothering Sunday on the fourth Sunday in Lent, also known as Refreshment Sunday as the strict fasting observances of Lent were relaxed.
"Mothering" initially referred to the duty to return to the "Mother Church" on that day, and later the day was adopted as a holiday for young people in service to have the day off to go home and take a present to their mothers. Often the present was a Simnel Cake, a rich fruit cake with almond paste. I remember baking such a cake for my own mother when I was a student, and surprising her on Mothering Sunday when I turned up at her door.
