I can't speak to the UK but in the US things like electrical towers and highway signs mostly go to tubular construction for labor cost reasons.

Tube gets manufactured in a facility specializing in doing it in a low labor way (rolling or whatever). Flanges get welded on, they get slapped on cribbing and trucked to you and then assembled with minimal labor.

Contrast with the lattice. Cheaper material inputs, a whole bunch of cheap channel with holes punched as needed, but all that punching, and then all that bolting, takes way more labor, a lot of it can be done cheaply, but it adds up, and when it does get to site there's more pieces to pick and connect, etc.

Basically the more expensive material saves you quite a bit of human labor at each step. Same reason huge rolled steel and welded tubes displaced riveted construction.