It's not really an easy answer as (1) it doesn't stop phishing attacks hitting work emails so isn't really relevant anyway, (2) most people, executives especially, don't want to cart multiple devices around, which is why we now have to deal with the security nightmare that is supporting work stuff on BYOD phones, (3) I don't work for a SV company with the budget to buy everyone two laptops, and if we did, honestly I think most people would prefer a better single laptop than two mediocre ones. Besides, most people just treat their phone as their personal portable device now. The odd person brings their own laptop.

Developers are the exception here, where usually they'd prefer to develop on a machine with minimal BS running, even if it means carrying around an ultraportable in addition to their development workstation laptop.