ISO 9001 specifies responsibilities for top management in the quality management system.
When you're in a tiny micro business with 2-3 people - everybody works together to get things done. There's lots of overlap in people's roles and it seems obvious that keeping the customer happy is everyone's responsibility.
As the business grows, the roles become more separated and specialised. Now you have a CEO, a sales manager, someone to look after the equipment, to manage projects, to do purchasing, manage accounts, etc.. Some of these people don't interact with the customers directly anymore. Do they have any role in the quality system and in ensuring customer satisfaction?
Of course they do!
Your people and processes are the engine pushing the car forward, and each part has a role to play in the functioning of the engine. If something is not working properly or doesn't know what it's supposed to be doing, then it causes problems for the whole business.
To run smoothly, an organisation needs systems and defined roles and responsibilities. It's up to top management to define these.
ISO 9001:2015 is quite clear about management responsibilities.
There's a whole section under "5 Leadership" where each requirement starts with 'Top management shall...'
This is different to most other sections of the standard where requirements say 'The organisation shall...'
Top management have the following responsibilities that can't be delegated:
(refer to ISO 9001:2015, clause 5 Leadership and clause 9.3 Management Review, for the full list)
Several items say 'ensure...', which means that top management must maintain oversight of these things even if the 'doing' has been delegated.
Essentially, top management sets the direction for the business, determines the structure or framework in which the business processes operate, and ensures those processes have the resources needed to generate their outputs and meet customer requirements - on an ongoing basis.