They ran in parallel.
The 200R (and the rare, earlier 200N) were the all-singing, all dancing water cooled, power valved, semi-YZ replicas, but the humble old 175 was kept in production as the cheap, simple, unpretentious beginner's/farmer's bike.
My nearest dealer still has a couple of 2006 model DT175s on the floor - apart from the front disc and the paint job, they're the same bike as Anna's 88 model.
Yamaha did the same with the single cam XT250K - kept making and selling them for years, in parallel with the disc braked, twin cam XT250N.