Earned income is income earned from working, from providing goods or services. Scholarships and fellowships are not considered earned income because it is considered a training position and you are considered a student, even if you go to the office or lab every day and do research or experiments that seem like “working”. Because scholarships and fellowships are not earned income, they are not subject to self-employment or Social Security tax and they do not qualify you for the earned income credit or certain other tax benefits.
As noticed by you and clarified by @macuser_22 , fellowships are considered compensation for purposes of making IRA contributions beginning in 2020. (They are still not considered “earned income” for other purposes, however.)
