In this context, meaning is essentially a long-term, or persistent, goal or aim. These, in turn, are more or less desires to change or maintain some state of affairs. One question is whether or why some have while others lack such desires. Another question is whether a person can be happy without having such desires.
If a person were to live in pure reaction, without long-term goal or plan, presumably the only meaning or purpose would be that implied by one's nature. In such "pursuit", one's purpose is essentially deferred to instinct. If one has faith that instinct knows the way, perhaps one can be happy in this path.
Moving away from pure instinct, one might defer purpose to ideology, religion, or God. A further option is allowing another person or group -- say a charismatic leader -- to guide the way. If one should fully trust the wisdom of someone or something else, why worry about the meaning of it all?
But for those poor souls having high need for cognition, a more involved approach may beckon. These creatures may be left to ask the hard questions, wanting to know the whats and whys of life and universe. Should one choose a belief system, that system must be understood in-depth. Purpose may become a deep personal affair.
The thing is, meaning is perhaps always present, even if only per instinct; yet it seems not everyone desires to dissect or systemise meaning. The technical difference may be one of instrumental depth, or how far removed or abstracted a goal or aim is from raw instinct.
For example, say we have two men of opposite persuasion who both desire to reproduce. On the one end, man A sows his oats and is thereafter fully satisfied. He feels good, and the job is done. On the other end, man B decides he has to find the perfect mate, after various schooling, followed by finding the right position in the right area. Then, after the children are born, he feels the strong need to help arrange the right schools, followed by seeking to provide guidance and other support for as long as possible.
In the first case, minimal instrumental depth is partaken; while in the latter, maximal. Both cases involve meaning. Both times instinct is the driver. But only one involves extensive cognitive consideration. Naturally we would expect most people to take a more middle road on their instinct-instrumental continua.
Heuristically, a correlation might exist between high instrumental abstraction and long-term thinking; yet in theory, these traits are independent.
On the topic of whether we can function without meaning, an important predicament ought be mentioned. If a person thinks long-enough-term, or with sufficient abstraction, sometimes conventional goals can appear or become futile. For example, if one's goal is to have an everlasting legacy, the thought of the Sun burning out may create a barrier in one's aim. In cases like this, a long-term minded person may need to modify or abandon certain plans and expectations, which may leave one wanting of purpose. Generally, these types of problems begin cropping up when we start questioning instinct -- when we seek too much certainty, or otherwise abandon faith.