It used to strike me as odd that my PlayStation and PS2 both had Panasonic optical drives, but looking back to my time in the aerospace industry, when we designed avionics packages for ordnance we'd generally use the most economical part even if it wasn't manufactured by us. Sometimes competitors just happen to hit that price/feature/specification nail better than your own products.
Sony used to be about more mainstream electronics, including RAM and processors, but it looks as though as they mosh pit of a market has become more crowded they have focussed on more niche areas. According to Sony's April 2019 Q4 statement, their semiconductor division is operating at twice the profit as their optics divisions (with Apple being their primary customer) and a little under half as much profit as Game & Network Services (i.e. PlayStation + Sony Entertainment Network).
It still remains weird to look at any Sony financial statement and see all parts of the organisation is profitable. How times have changed.