Marketing budget? Good distribution?
What technology-related point are you making?
If you ask a member of the Church of Apple, yes, you'll get that answer. Ask any heretic and they'll give different answers ranging from 'I want to keep things separate so I don't flush my PC down the loo next time I forget to take it out of my back pocket' to 'I want to keep my PC personal and don't trust ${vendor} to abide by that promise'.
As to 'Samsung' (or, rather, Android) being 'insecure' it is remarkable to see this premise being pushed. From what I gather there is not much difference between Android and iOS in 'security' - if anything it seems to be iOS which is more often in need of patching against yet another 0-day/0-click related to problems with iMessage or other text-parsing related bugs where Android 'security' problems seem to be more related to the lack of updates for older devices.
But, demand is created by early adopters (the people here), and those people don't use DEX because they don't use Samsung, due to Samsung being considered janky-to-insecure, depending on who you ask.