Now there are so many projects, and there are various names of new tokens and coins. even many projects seem almost similar to each other.
while the bounty is one way of promotion, which aims to strengthen the relationship between the developer and the community. thus, more people are expected to know about the project (tokens / coins).
so in my opinion, even though these tokens / coins are already listed on the exchange. bounty as part of promotion is still needed, so that the tokens / coins are not "forgotten" with the emergence of many new or similar projects.