Delight. The network airlines will reaccomadate missed connectection on subsequent flights. This is just one example where the airline is not being paid twice for the same seat.
Economically and environmentaly it is a sin to let a seat go empty.
Every one of us who have ever flown on a full flight have benefitted from oversales. We just don’t know it.
And the average airline still only makes a few bucks per passenger, the locos do better but their ROI is still nothing spectacular.