The goal of software architecture is

>> cost reduction

> fulfil the quality goals

I’d word it as “keeping the cost of changing software low over the long term”.

I don’t think you can reduce that to a quality goal of “modifiability” because it’s not negotiable like other quality goals.

I don’t think you can say it’s just cost reduction, but that is closer.

It’s an existential thing. Architecture is about retaining the ability to change your software (avoiding the big ball of mud). If you lose the ability to change within time and resource constraints then the project, product or startup is dead.