Security solutions for embedded devices are where RTOSes were in the 1980s. A few commercial solutions have started to appear on the market and customers are left with the choice of rolling their own solution or adopting a commercial solution.
Early on, many companies rolled their own RTOS. Over time, this gradually changed with commercial RTOSes becoming a larger and larger percentage of the market. Eventually, quality open-source solutions became available, providing yet another option for developers.