Cutting back on free seating in the airport departure area increases the amount of purchasing expenditures passengers make at airport.
Airport owners/operators -- and sometimes even the main airline tenant in a terminal -- get a piece of the retail sales revenue pie in some form or another.
Combine this together and it's no surprise that airports increasingly make passengers go through a shopping mall before getting to the gate areas with a lower proportion of free seats vis-a-vis departing passenger counts.