Corruption is something quite endemic throughout Chinese history and something of a revival after Deng’s open door policy. A lot of old attitudes that were not existent under Mao began to crop up. Its somewhat a result of new economic opportunities and the officials being in the right place to cash in on them. Lots of laws and bureaucratic red tape means some things cant be done or you need to stand in line to get it done. But a little bit of money can smooth things over quite quickly.
China actually has a reputation of having a certain level of corruption. The anti-corruption campaign has helped, but it will need more reforms and a harder impact before it looks like Singapore.