Why had people bothered to build a bridge when there were boats and flyers to ride?

The quote is from Ursula K Le Guin, ” A Man of the People”, the third of four novellas that comprise Four Ways to Forgiveness.

Having sketched this quickly, I now see her iconic bridge is different in scale, described as enormous, reaching far above a landscape of tidal pools inhabited by myriad wading birds, descended originally from those brought from Earth.

It is old, maybe a million years.   So, I guess, it was built across a long-changed landscape, and likely by machines and labour controlled by strident imperialists, alien to the contemporary pueblo-dwellers with production divided by gender, lineage and tradition.