The title attribute may not be read by all screen readers by default, if at all. Some will, but some won't.
Additionally, when users are keyboard only, touch input, or using voice access they may not have an easy way to view the content contained by a title attribute. Whereas assistive technologies beyond screen readers can make use of it.
Users with fine motor impairment may be unable to hover long enough to show a title, depending on their browser.
Labelledby has the highest precedence in parsing, and every screen reader will know what to do with it. It removes uncertainty as a dev -- you know absolutely what will be read by it.
Aria labels can be used to give blind users the same experience as sighted users, which may not be the same text as a tooltip. If you need to convey something visual about the item being labeled and some text, you can use aria attributes to provide that.
Title gets inherited by all children, unless a child has an empty title. This could cause weird behaviors for screen reader users if one isn't careful. Labelledby is not inherited, and gives you control over which specific elements get labels.