Only children usually get too much attention at their home. When they grow up they try to maintain that level of attention they used to get at home by getting it from different sources. Only children are very likely to become showy.
The youngest kid usually gets more attention than the elder ones since he is always seen by the parents as the weakest one. As a result youngest children might turn into attention seeking adults.
Some people seek attention because they feel insecure. They want to show their best to others to get over those feelings of insecurity.
Some people think that they are unnoticed, as a result they do their best to catch the attention of others. If a person believed that others overlook him or that they don't think highly of him then he might become an attention seeker.
A person who has a low self esteem might turn into an attention seeker. When that person gets some attention from others he usually feels a bit more worthy and thus he gets addicted to the attention seeking behavior.
Just like over attention can make a person an attention seeker neglect can also lead to the same result. If a child was neglected by his primary caregivers then he might grow up into an attention seeking adult. In such a case that person tries to get some of the attention he was deprived of.
Narcissists usually want to get everyone's attention. They hate it when someone else shines in their presence and that's why they might go lengths to seek attention.
Some people seek attention when they feel worthless. Those people usually lie, tell exaggerated stories and go lengths to make people think highly of them.
Some people seek attention when they believe people consider them worthless. In such a case the main goal behind the attention seeking behavior is to show that they are truly worthy.
So many attention seekers do it for approval. Those people are usually in need of extra approval because they have self esteem issues. The attention seeking behavior helps them get some attention and so remain psychologically balanced.
A person can seek attention when he feels jealous. This is usually very common between young siblings where a child tries to get his parents' attention because he is jealous of his brother.
If the parents favored one child over the other then the neglected one might develop an attention seeking behavior. The attention seeking behavior in such a case is a defense mechanism against the neglect this child was subjected to.
The Histrionic personality disorder is a disorder characterized by exaggerated attention seeking and unpleasant feelings when the person is not in the center of attention.
A person who has self doubts might try to get attention from others , especially new people, to make sure he is still attractive or interesting.