On the way to Bugis

My train from Pasir Ris docked into the centre lane of tanah merah station,which was the expo/ airport lane. For a second I panicked, I'd thought that I took the wrong train. Then I got angry at myself for not checking first. Since, you know, MRT trains break down on a pretty regular basis. The announcements then came on. It's really to Joo koon. Whew. The train operators were repeating non-stop that the train was to joo-koon. Annoying. Why didn't they go to the normal lane?