DTube is different on the back end technology wise, but the practical reasons are at the very least:

1. Content creators are paid using the Steemit, steem currency model instead of the ad revenue model. That means their content cannot be demonitized by the platform.
2. Content cannot be censored by the platform. Copyright, libel/slander, etc. claims can be filed of course, but that is(presumably) between the company filing the claim and the company hosting the video.
3. DTube offers diversification away from Youtube, which is virtually a monopoly due to other alternatives sucking either through poor UI, poor community involvement, poor monitization scheme, etc. So if Youtube were to fail, it wouldn't be game over.
4. There is no banning/termination mechanism that I know of on DTube, so creators won't wake up one morning to find their accounts have been locked/terminated like they could on Youtube.