The bean counters that run these programs probably don't see it your way. Also, I don't think very many people see the expiration as a deterrent, nor would it be a major factor in which company they choose. If someone has a career change later on that suddenly necessitates frequent travel, they would be starting from square one regardless of program.

People who don't patronize these businesses often enough to maintain the points, are most likely to book on price anyway. Even then, the expiration on the points are fairly generous. Anyone that cares enough about program benefits are most likely going to participate often enough anyway. If not, they'll simply go with whoever is the cheapest.