Many invest in a country usually not because of the people who excel in mathematics. but they choose where it is strategic and the production costs are low. for mathematical intelligence it is related to how the individual's career will be, not with the country
I agreed with what you said because companies or groups that invest in country that have huge number of students winning the Olympic award in mathematics while the country itself dont have the required resources, commended tax per production and infrastructure the investors or company will bankrupt, so OP the companies that moved to the Southeast Asian countries dont actually moved of they have numerous students that won high prizes in Olympic math.
Yeah, every business excels in favorable tax laws and other important aspects and if a country has bright students in mathematics or studies in general that would not matter as much as the taxation policies and the transportation cost influences.
Cheap labor and cost of electricity are among other important aspects when a company decides to open their headquarters or offices in a particular country and it is obvious that every country has good and bad students/employees so that doesn't matter as much I think. I don't know if OP is true about Samsung moving it's factories from China to Vietnam but if that's the case that might be because of the cheaper taxation there.