Adding a UK take here: In my area in the South East of England, we have overhead power (and POTS) on poles down the streets. Recently Openreach have been stringing fibre alongside the existing cables.

Virgin Media (the other provider) just dug trenches in the pavements about 20 years ago.

Added bonus of having overhead power lines? Your lights flicker when it's windy...

My fiber line (Mountain View, CA, US) is aerial and uses the same poles as electricity. Strong winds cause tree branches to break, which in turn often cut wires. So, they might, but it's less robust than underground, which results in more maintenance and more operational costs to the internet provider.

The power company where I live installs more ducts than they need when they dig a trench. So they'll install say 10 ducts in the trench when they only need one or two. They rent out the extras to telecoms.

In my neighborhood in Seattle all the Fiber cables hang on utility poles. Is that what you mean by aerial?