Political incumbents have advantages which preserve their ability to stay in office -- access to funds to overwhelm underfinanced challengers, paid staff that tend to constituents' problems, government privileges which provide opportunities for self-promotion, often as "official business", access to research and media, and carefully gerrymandered districts that ensure solid blocs of support on re-election day.
98% of incumbent congress members in the USA who seek re-election have been successful in recent years. For example, in 1998, House incumbents ended up running unopposed in 95 districts, while in 127 they faced only token opposition; a record 98.5 percent of them were reelected, collecting an average of more than 70 percent of the vote.
In an ideal world, a people that reelects almost 99 percent of its leaders would seem to be happy with them. But in the real world, you only have to win once to become a permanent fixture in a rotting political establishment.