Comment by zimpenfish

Covered quite well in other comments but: health and safety, working around existing infrastructure, political constraints on throwing money at problems[2], lack of skilled workers[1], etc.

[1] e.g. Crossrail hit delays because other projects like Spurs' new stadium were willing to pay 2x the daily rate; https://www.newcivilengineer.com/latest/crossrail-boss-blame...

[2] Although if you can convince politicians that infrastructure helps fight terrorists/blocks immigration/lowers taxes for the rich, you'll probably be drowning in money pretty quickly.