Because new 'lands' aren't just a row of rides with a generic thematic link (anymore). They are fully themed with other attractions, shows, M&Gs, restaurants, restrooms and immersive scenery which takes up a lot of space. Of course, the counting of "rides" is the mentality of someone who really doesn't appreciate the "theme" in "theme park." These are folks who hop through all four parks in one day hitting just the rides and complaining that there's nothing to do.
But, since you asked 'since when'...
Storybook Circus: 1 new ride, 2 converted
TSL: 2 new rides, 1 converted
Hogsmeade: 1 new ride, 2 converted
Diagon Alley: 2 new rides
New Fantasy Land: 2 new rides
Cars Land: 3 new rides
Pandora: 2 new rides
SW:GE: 2 new rides (both E-Ticket)