We tend to try and find meaning, even when it doesn't exist. This is why you have cases of things, such as adventitious reinforcement (behaviour that is accidentally followed by a reinforcer, causing the behaviour to increase despite the reinforcer acting independently of it. A good example can be seen with superstitions. This also isn't human-specific and can be observed in animals, such as pigeons). Hence why a lot of people believe that there has a be a creator(s) and that there is no way that their existence was just the result of a series of events that happened by chance. In their minds, there has to be a reason for all of this. Thus, people are constantly scrounging around, trying to come up with some sort of idea as to why we are here. That's why religion is so popular. It offers people answers and provides them with that sense of meaning that they were looking for.
"You woke up today because you have a purpose" is something that is said because of an inability to reconcile with the fact that purpose doesn't exist. Not everything has a meaning or purpose and meaning doesn't even really exist outside of the mind. People are looking for connections that don't always exist. You will die and everyone who once knew you will die and one day the entire human race will go extinct. The idea that there isn't anything more to life is terrifying. It's much easier to give into your urges and believe that you have a purpose and that you truly mean something and that everything happens for a reason and that if you are good enough you will eventually be rewarded in some sort of afterlife.
Basically, people tend to try and assign meaning to things, people have a hard time coping with the idea that life might be meaningless, and thus they end up convincing themselves that they must be here for a reason and their life must have some sort of objective purpose. We are predisposed to making meaningful connections and most have a need to try and avoid having an existential crisis.
I think people make these sayings as ways to encourage people to keep living, give them empty hope, and blah blah. It's just rubbish, and I'm sure they don't even know their purpose!
