I think why many altcoin projects have failed because they only sell coins and give some bonuses to each buyer through sales, but they don't offer a long term program that they will do in the future. because I think many investors are interested in projects that have long-term prospects by launching various programs and products.
Actually, bonuses in the selling phase aren't a problem as long as the project has a long-term program that can guarantee for the development of the project and the token value. Sadly, as you know that many new projects only focus on marketing for the selling phase. They prioritize only for selling all their tokens as much as possible. Even worse, if the project has no product offered for a long-term goal. We simply can guess that the project will fail or won't survive a long time.