Read on insulators and AC insulator losses, insulator aging, cost vs. air. Or ask your favourite LLM.

A few bird shaped pylons near busy roads is probably nothing compared to miles of HVAC or HVDC cable and normalized insulation losses spread over its lifetime.

Also the branches in the sculptures are used to break lightning into smaller electric arcs just like in regular pylons. Pretty cool. Very Victorian.

https://www.youtube.com/watch?v=tWYxrowovts