I believe mothers and parents forget that "Life is a personal journey". They also forget what it was like to be a child and craving independence and freedom.
From their point of view they still remember you being the infant who had to rely on them for everything. Their sole responsibility was to look after you and protect you from the evils of the world.
Eighteen years come and go in a blink of an eye and suddenly the "calendar" says you are an adult but your parents aren't ready to let you go. They wonder if they taught you everything you needed to know before stepping out in the world alone.
As much as they know on a intellectual level that each of us has to learn from making our own mistakes they still find themselves trying to (protect you from you).
Mothers never stop wanting the best for their children.
Most of them start to let go and trust you'll be all right around the time you reach your 40s. (Assuming you're no longer asking them for financial help)ha ha ha