I don't think thats really true, Audemars & Patek deffo made entire watches in the 50s.
Don't get me wrong they also designed movements, but by the time of the quartz crisis, Patek bought in movements from outside.
It doesn't really help that omega and tissolt were merged with Certina, ETA, hamilton when then turned into swatch, which basically dominates the entire swiss watch industry along with rolex and richemont(who own Vacheron)