Iterations in hardware businesses are far more expensive, particularly for early stage (by revenue not age) companies like Blue Origin. Outside of the Vulcan engine sales, joy rides and NASA grants they don't have much inflow and depend on equity infusion.
SpaceX also would find it tough without Starlink revenue to fund iterations for Starship. Similarly the early customer revenue ( plus the generous NASA grants) contributed to iterate on F9 be it Block V or for landing etc.
Beyond money, it also requires the ability to convince customers to be okay with the trade-offs and risks of constantly changing configurations, designs.
It is not that people do not know iterative testing with real artifacts is quicker, but most are limited in their ability to fund it or cannot convince customers, regulators to allow them.