How do winner take all voting districts serve as a structural barrier to third-party and independent candidate success?

The winner-take-all voting districts serve as a structural barrier to third-party and independent candidate success as the larger political parties incorporate the agendas of the third-parties and independent candidates with their own agendas.

Explanation:

The agendas taken up by third-party or independent candidates majorly speak about local issues concerning the local populations. These issues are devised by the candidates of larger political parties and are included in their own agendas. This act of the larger political parties serves as a structural hindrance in the success of other small parties and independent candidates.