MPL holders earn a portion of the fees that Borrowers and Lenders pay to the Maple protocol. All Maple Token Holders earn a share of the Establishment Fee which is accrued to the Maple Treasury and distributed periodically. This fee is paid by Borrowers when their loans are funded and is shared between Pool Delegates and Maple Token Holders.
MPL holders do not need to stake their MPL in order to earn their share of the Establishment Fee. If MPL holders want to earn additional fees via participation in the Ongoing Fee paid by LPs, they can stake their tokens.
You can view the MPL Scenario Calculator here.