It depends on the type of software. A B2C SaaS that has continuous small releases with easy incremental deployments and rollbacks is incomparable to a bespoke B

It depends on the type of software. A B2C SaaS that has continuous small releases with easy incremental deployments and rollbacks is incomparable to a bespoke B2B release that integrates with dozens of the customer's other systems. The latter are typically deployed over the weekend with multiple companies/teams on standby as unexpected interactions are at a certain point of complexity a given. Your quality aim is for instrumentation and verification to rapidly detect and access and triage issues since assuming you can hit 'deploy' and walk away because your code is perfect (delusional) ignores that 95% of the systems you integrate with aren't even under your control, and 'it worked in test and was signed off' is not an acceptable answer for a client's production system being down on Monday.