People say this, and yet we see vacancy everywhere all the time.

The last ~10 times I've flown have been completely maxed flights. I can't remember the last time I saw an open seat anywhere.

Yep, post-covid it seems like airlines are favoring fewer flights that are more packed. I don't fly a lot (couple times a year), but when I do, it's very rare to see a flight that is not at least 95% full.

Yeah, for the routes I've flown over the last 5-10 years, significant numbers of empty seats are very much the exception rather than the rule, and it got worse post-covid.

I remember a Lyon -> Bangkok on A380 on April 2nd 2010, we were 50 in the plane (capacity 530). Less than 10% full. With 20 stewards.

Eventually there just isn't someone who wants to go at any price, but the airplane still needs to fly.

Overbooking is still an industry standard approach to profit maximization. The opportunity cost of being overbooked (rebooking/refunding) is way lower than having a few seats empty because of the average cancellations.

tl;dr - airlines are happy to sell you a seat that's taken, betting some % of other people cancel.

Curious what routes you fly, I have been on full flights consistently in the past few years, mostly Boston to Denver

I haven't flown in a number of years, but when I was, it was common knowledge that all airlines intentionally overbooked their flights. If you ended up being one of the unfortunate last 5% (or whatever) to check in, you were effectively turned away and offered a voucher for your trouble.

Is that still done?

A friend was bumped on a full flight from London to Europe last week because he didn't check in early enough, but I haven't heard of it happening on the continent side.

As far as I know this is a true American problem, I have never heard about this, or have experienced this in Europe or Asia.