SEOUL, South Korea — When Lee Jae-yong, the de facto leader of Samsung, walked free on Monday after spending barely a year in jail, it reaffirmed a pattern South Koreans have fought for decades to break: Business tycoons convicted of corruption here hardly spend any time behind bars.

Mr. Lee’s arrest a year ago, and his subsequent conviction and sentencing, were hard-won victories for millions of protesters who took to the streets from late 2016. The demonstrations also felled President Park Geun-hye, impeached on charges of collecting bribes from family-controlled conglomerates, known as chaebol, like Samsung.

But here in South Korea, Mr. Lee’s detention was as big a piece of news as Ms. Park’s ouster. His father — Lee Kun-hee, the son of Samsung’s founder and the conglomerate’s chairman — was twice convicted of bribery and other corruption charges but never spent a day in jail, creating an image of Samsung as untouchable. Many South Koreans hailed the lower-court ruling, which sentenced the younger Mr. Lee to five years in prison on corruption charges, as an important milestone in their country’s long-running campaign toward greater transparency and accountability.

So when an appeals court freed Mr. Lee, 49, on Monday by reducing his prison term to two and a half years and then suspending it, the scene was dishearteningly familiar for many.