why is it that incumbents are rarely defeated in their House districts when running for re-election—with many facing no significant opposition to re-election?

In modern politics, why is it that incumbents are rarely defeated in their House districts when running for re-election—with many facing no significant opposition to re-election? Order Description -Double Spaced -Times New Roman, 12 inch font -One inch margin -APA -Only using a quotation sparingly—and only if memorable and not more than a single sentence in length. Limit to a maximum of one quote per page in your papers -Do not use cover pages, sleeves, and jackets. - Scholarly sources