I think the team might do their own advertising for fund rising for their project because they are confident to reach the target of fund rising, one other reason also behind not to conduct bounty is team might convinced big investors to invest in their project so no need to conduct bounty. Some projects have lower budget for marketing and lower capital to rise, they do only airdrop. Some new project might not aware about bounty or not willing to give their tokens to bounty hunters and they doesn't not know that bounty campaign is just a part of marketing of their project with huge community on social media.