What prevents companies from adopting security-first approaches during software development?

Hello community,

I recently launched a tech startup alongside two developer partners. While they focus on technical implementation, I manage business operations and am researching major challenges organizations face when building secure applications.

I keep wondering about this question:

Why haven’t security-first methodologies become standard practice across the industry?

What barriers prevent organizations from integrating security measures from day one? Could it be budget constraints? Timeline pressures? Knowledge gaps? System complexity?

I’m interested in hearing your experiences, whether you work as a developer, engineering manager, security specialist, or consultant.

Just looking to understand the landscape better, not promoting anything. Appreciate any insights you can share.