How many hundreds of thousands or millions of km of trenches though do you think you actually need to serve the entire rural world? How long do you think that would take? That 750km trench might only ever serve 500-1000 people, hence why it never gets built.

Starlink and the LEO constellations provides the capability for anywhere in the world that can clearly see the sky, to have internet. Today. The next stage of the network will make that capable of serving everyone in rural areas instead of having some cell capacity limits on people as the V3 dishes provide 10x the capabilities per dish, and 20x per launch. The only reason not everyone has access to it is because of geopolitical reasons and licensing, but it could technically serve the entire worlds rural areas today.

For the non land areas you can't just wish wash that away with 'future tech' or it's not important. Keeping hundreds of thousands or millions of drones up in the middle of the oceans isn't going to happen. Sea internet is just as important to the millions of people who work or live on the sea as it is to the rural people at home. The dramatic improvement in quality of life at people at sea is also improved, and has even been noted by the military.

Surprisingly, Starship is actually 'clean' in terms of air pollution. It's exhaust is just CO2. They could in the future pull CO2 out of the air via solar to make the methane making it neutral. So it's still a global warming issue, but it's not tossing other noxious compounds into the air. It's also a tiny fraction of current airline usage. There's more CO2 emissions from 1 day of transatlantic flights, than it would take to maintain and grow starlink each year with starship.

Edit: and in case you missed it, starship is operational now. They launched 10 functioning satellites on the last launch. Its a long ways off from being fully and rapidly reusable, but it can deploy payloads now.