Ignorance is the lack of knowledge or information. Motivated ignorance is the state of ignorance and the desire to remain in such a state. Humans from 5000 years ago might not know that Earth is a sphere, but they are different from modern flat-Earthers. Flat-Earthers are not just ignorant; they are motivated to remain ignorant.
An ignorant person is unaware of a fact or information. A motivated ignorant person is unwilling to know and refuses the fact.
Ignorance is easy to fix by providing the information they are unaware of. On the other hand, motivated ignorance is difficult to fix as the person tends to avoid unwanted information.
An ignorant person will defer to the experts on the things they cannot understand. On the other hand, a person motivated to be ignorant will discredit the experts on the things they wish to remain ignorant about. Everyone is not an expert on everything and will defer many things to the experts.
Flat-Earthers do not know Earth is a sphere not because they honestly do not know it but because they are motivated to remain in such a state. They do not lack the means to know the fact; they willingly refuse to know. The desire to channel their prejudices provides the motivation to remain ignorant. It is the reason why it is so difficult for flat-Earthers to escape from their ignorance.
References
- Willful ignorance – RationalWiki