Intel also exited the Microcontroller sector years back, as their R&D and cost models simply did not fit.
The intel invented 8051 continues to be profitable for many, and is now available down to MSOP10.
Zilog have a 8051 family and there is even an 8051 (S3FI1BG) in Samsung's stable.
That said, most of Samsung's parts are niche-custom cored, which will be very hard for IXYS to support, even without adding the Korean :: USA gulf.
One also hopes IXYS have read the foundry-side fine print, very carefully indeed.
I think it's a case of "Size matters". When you're Samsung, a market has to be really big to make it worth your while to address. The revenue for their 4 and 8 bit MCU business is pocket change to Samsung, and probably not a market they can make actual money in.
It's a market Ixys *does* think they can address profitably, and as a much smaller outfit with lower overheads, they may be able to.
Samsung is not selling their product line because it doesn't fit their direction, they are selling it because it is not profitable. This may increase Ixys revenue, but it won't help their profitability.