There are a lot of projects that conducts IEO and competition is very big. To attract investors it is necessary to have more promotion that competitors have.
I agree that promotion is important, but promotion must be resultative. It is possible to spend money for promotion without any results.
Promotions are very important for any project, bounty activities will help the project to get awareness about their IEO. This will really help project to collect enough money for the rest of the developments what they mentioned in the roadmap.
It is true that the bounties also promote the project well let alone IEO they might invest, see IEO Auditchain in many shortex who invest.