Thats because there is 0 additional marginal cost for their salaried consultants' time, too. Like many in the workforce, they are a paid a salary, and it's the same amount whether working 40 hours or 80 hours.

No... that's not a good explanation. While it is true they're salaried, there are plenty of professions that bill by the hour for the time of salaried employees. How you bill doesn't need to match how you pay salaries. It could also be billed per day of work regardless of the number of hours and the issues mentioned above would still be pertinent.

Isn't unpaid overtime illegal?

Not for white collar, FLSA-exempt employees! And boy is that a broad umbrella!

See: https://www.dol.gov/whd/overtime/fs17a_overview.pdf

Not if you're an exempt employee!

It's only illegal if your total salary would work out to less than minimum wage. Working 80 hour weeks year round at WA's 2020 minimum wage works out to $70k a year if you include time and a half after 40hrs/week.

Your job isn’t to do X hours of work your job is to meet a goal, objective or target. You don’t get to stop when the clock hits a certain hour in this industry.

Not if the position is overtime exempt.

I'm not sure if this exists in EU. Does anybody know of a similar situation in EU?

Absolutely does. Everyone just signs to opt out of the 40 hour (something like that) working week directive and contracts are clear that there is no such thing as overtime.