Neocolonialism occurs for a number of reasons. Among them are:
Imperialism is no longer acceptable in the eyes of world public opinion. Rich countries cannot simply take possession of poor countries anymore. Therefore, neocolonialism is necessary if rich countries are to control poor ones.
There are still poor countries. If all countries of the world were wealthy, there could be no neocolonialism.
Capitalism dominates the world economy. This gives rich countries and firms in those countries the incentive to go out and try to exploit the resources of poorer countries.
These are the most important reasons why neocolonialism exists today.