Few people had a need for it, so few people used it, so Google didn't care.

That's just changed as they try to bring the hammer down on ad-blockers and people are scrambling around looking for new ad-avoidance methods.

Having multiple profiles with separate channel subscriptions is a nice feature. Google should have added some way to organise/group subscribed channels long ago really.

There was a period of several months not all that long ago where they didn't work. But they're back now.